1,You need a software which can decompile,compile,sign apk.
2,Only games that is based on unity game engin can be converted.
3,Open lib folder of any apk if there is unity libs then it will be converted.
4,Now have to understand that game created on which version of unity(like 3.0,3.xx etc).
5,Unity engin support Armv6,Armv7(not 4.0).
6,Now you have to replace the correct libs with correct version of unity.
THIS IS A BIG CLUE DON'T ASK ME FOR MORE BECOZ I LL TAKE AROUND 3 MONTH TO KNOW THE CONVERTING FULLY AND I DON'T WANT TO RELEASE FULL STEPS..
IF YOU HAVE.BRAIN THEN YOU CAN CONVERT GAMES WITH MY CLUE.