Witch memory are you talkin about?
RAM, you cannot do anything unless removing bloatware.
Storage aera, you can try to move some apps to external sdcard or use the preload partition.
Anyway, phone slowing down is the sign of low RAM, so you should try to remove apps you are not using.
Search here in XDA for apps safe to remove like "social hub", "music hub" and so on.
Remember that you'll need a rooted device to do so.