Android Update has made phone slow and unuseable

after update to android 4.1.2 my galaxy ace 2 has become extremely slow, unresponsive etc..

(1) Has anyone found apps causing this following the update

(2) Is it possible to increase the memory on the phone ? ( I am a trained electronics technician so can replace parts - but will the software deal with it and is a chip to replace the memory available that is of the same package type ?

(3) Has anyone had this problem and managed to get samsung to admit its software update has made the phone un-useable ?