Go to your inventory screen showing stats. Highlight Health and press black, white, black, black, black, hold A until health rises to full.
Increase Armor Skill
To increase Armor, find some enemies that do not do much damage and get hit by them.
Increase Athletics Skill
To increase Athletics, run around until your fatigue bar hits 0. Then, wait for your fatigue bar to raise to full and repeat.
Increase Block Skill
To increase Block, hold chop while using a shield and get hit by enemies.