To gain access to all the suit upgrades you must collect the 15 red bricks from the hero missions. The locations below have been done in free play, as it's easier. Hope they help.
Red brick locations:
1-1 - At the end of the level whilst you fight clayface, it is inside the safe at the far left corner, smash the panels to get the red brick.
1-2 - Inside the factory, after you have crossed to the other side, they will be a part when robin has to use his metal boots, just after he does in the back will be a glass chamber, double jump up and use a strong character at the top, then jump down and smash the red thing. jump onto the switch and chnge to the 2nd player to get the brick.
1-3 - As you fight Two-face, if you go to the top left corner of the level you will see a green barrel, shoot it and the grab the red brick.
1-4 - In the Lab/Workshop area of this level you will see shiny metal things in the back left of the area, demo these to build the joker station. Switch to joker, use the joker station then use the two other switches to the left of it, once done the glass to the right of the station will open and the red brick will be inside.
1-5 - Once you've made your way into the bank and you've dealt with the first bottom half of the screen. go over the bridge and choose a acid character like poison ivy or joker. then go left into the acid, smash all you can see, then place the buttons into they're holes. Once done stand on the buttons in the order: red, blue, green, purple. the safe will open walk into it and you will grab the red brick.
2-1 - As soon as you enter the next area, after jumping down the hole of the roofs, it will be to the left of you. Switch to blue batman and break the glass.
2-2 - When fighting against the ship at the end, grab some batbombs and head up, when through the fence swtich to a submarine and go under the blocked path to the right. shoot the 4 targets and the red brick will get delivered right inbetween the targets.
2-3 - At the very beginning of the level, use robins techno suit on a panel at the back. This will allow you to control the boat. With the boat you have to hit the 3 bouys very quickly. I suggest you hit them going left, then right then towards robin. The red brick will appear behind robin.
2-4 - In the second area, towardds the back at the beginning of the area you will see a broken staircase, double jump up them. Then use batbombs or peguin bombs to blow the top off and use robin diver to get the broken red brick, now fix it and its your's.
2-5 - Whilst fighting the penguin, go to the right of the screen, you will see a glass sheet, use blue batman to destroy this. once inside the tunnel, use grappel hook to get to a lever, hold on until its fully done. this will drop penguins onto 2 of the 3 runners. walk over to the first runner and do as the penguins do...run. You will see the red lights turn green once they do go to the right and jump on the button, the red brick will appear behind you.
3-1 - After the first section, you will come to a point where on the ;left will be acid with freezer sparkle going on. Freeze these 2 sections to help climb over to the other side. Now break the glass in front of the 3 enemies with blue batman. Next you will see 3 switches, the squence in which to be pulled is: Red and Blue. Blue and Yellow. Red and Yellow. It will appear infront of you.
3-2 - In the first section, keep running right until the end of the dock then jump over to the other side, or swim, and press the lever, this will open the gate.Now go in and switch to techno suit robin and press the techno switch.Now guide the arm to the pink teddys and use B to pick it up and drop it in the bottom left corner. Destroy the teddy and grab the others. Once done 3 times, the red brick will appear in the machine. use the arm to get it.
3-3 - In the second section (after blowing up the gas line) at the back will be green gas blocking a section, switch to joker helicopter and destroy the pipes and walls to gain access. Now keep shooting the twisty thing on the left to make another one appear. Shoot the new one to make a red canister appear at the back, shoot that and you shall recieve a red brick for your troubles.
3-4 - In the third section of the level after the blockade will be breakable things to the left, smash them and red pieces will appear. Switch to red batman so you dont die as they are heated pieces, build the ladder and climb up. Once up glide over to the other platform and double jump up to get the red brick.
3-5 - Once inside the tower, go to the right and destroy the purble box and fix the switch. press the switch and jump to the other side. go up the stairs and switch to glidey batman and glide over and continue up the ladder. glide over to the other side and then drop down 1 floor. switch to a strong character and move the organ then keep jumping on the button to make a person appear and you will get the red brick.
If you need more help let me know.