Do i need more ram? On idle my ram is at 60 percent and when im playing League of legends it go to about 90 percent.

How much do you currently have?

2 GB

Yes 4Gbs is the minimum thesedays to play games it's nicer to have 8gbs but you can get by with 4gbs.

What cpu and motherboard do you have? and are you running 32bit windows?

Yes, I recommend 8GB, or whatever the max is that your motherboard supports if it is less than 8GB.

Hp dc 5750 SSF

AMD Athlon 64x2 3800+ 2.0 GHZ 

2 gb RAM 

Windows Home Premiun 64 bits