There are two methods of getting this, it is recommend that you do a manual
Quick Save before trying either:
1 - Killing Innocent Civilians - Go to a large city and begin swinging your sword to kill anyone around. You bounty level should rise. If a bounty hunter comes near you, just run away to avoid the fight, and continue killing civilians. After 2-5 minutes, you should be at the max level.
2 - Killing a Leader - If you manage to kill a leader in front of witnesses, your bounty level should immediately shoot to full.
After getting to a level 5 bounty, feel free to revert to the quick save from the beginning of the guide. You can also try to kill all the bounty hunters or pay out the bounties using Drachmae.