[Q] PLEASE Help my device! topic

My Samsung galaxy S4 since update to Android 4.4.2 .The Device become very slowly and lagly . I have already tried many ways,but They do not work.
So Must I got root? I do not want to root,because I am afraid after the root device will cause instability and cannot update the newest system(such as android 5.0). Please give me some great advice!