EDIT: This is kind of missable as if you don't get enough points to buy an attribute you can then only get points by buying them with cash or using the app on Android/IOS to get some points. (Thanks Dream Fiend).
In your first game make sure to play well, pass and assist, play tight defence on your man, and don't try for 3 pointers and you should get a decent enough rating. Best to buy after the first game as you can lose points after that. (Thanks Enter gamertag).
After you've played your first game you can go into the 2K Store at the main menu. You will have received some points for playing your first game. (I got 500).
Go into MyPlayer - Attribute Upgrades. There will be various upgrades and depending on the type of player you chose will cost anything between 150-500. Choose one of these by pressing up on the category - add to cart with
, Open Cart with
and checkout with
Also if the servers are being dodgy you can use my player inventory - NBA/PRO-AM ANIMATIONS - NBA RITUALS - Press X to open 2K SPORTS STORE, is an option in the lower left corner, thats how I got into the store and bought the upgrade with points won. (Thanks xSTAGGERxLEEx).