What can I do to improve my regain/improve my computers memory?

My almost new pc has been running very sluggish lately, so I decided to go with a full system scan and repair with System Mechanic Pro. It finished its job and removed alot of unneeded files and restored some disc space,however even after defragmenting I still have only 10% of my total memory available. Subsequently, my computer is still running slow. Could this be the reason, and if so what can I do to get some memory back? Thanks in advance for your time.