Advise me please

My system:

Gigabyte S-series motherboard GA-MA78GM-S2H

Processor - AMD Phenom 8450 triple core speed 2104.

Memory 1790M

I want to upgrade to a faster CPU, the board will support AM2 Athlon AMD64 series. I want to be able to cope with facebook games, because at present they keep freezing and running very slow. Please recommend a suitable CPU upgrade and any relevant advice.

Thanks in advance.