how to get low mb low spec resources?

the default on my phones are 1.2gb on low spec and 1.9gb on HD but how can i get lower resolution than that? on 3.8 first i got same 1.2gb but later i got 600mb lowspec and 1gb HD with these resources phone didnt heat and ran smoothly. Anyone know how to get 600mb 700 or 800mb on lowspec? also What size did you get?