Change or not my cpu...

Post a budget please.

About 300 euros maybe a little more but around there...  

If your phenom 555 works with all cores unlocked, then the answer is no. But here is the best upgrade you can go with if you already have some ddr3:

http://www.ebay.co.uk/itm/Intel-Core-i5-2500K-3-3GHz-Qu...
http://www.ebay.co.uk/itm/Asus-P8Z68-V-LX-Socket-1155-O...

If you need ram: http://www.ebay.co.uk/itm/Kingston-8GB-2x4GB-DDR3-1333M...

Phenom is working with all cores!!How about GPU??

That's wide open; newegg must have 300 or more video cards. EVGA and a few models have lifetime warranties for registering online. And I would post a separate budget for the video card and list your favorite games. You can get a decent ddr5 1 gb card for around $125.

your unlocked phenom is more than enough for gaming but your gfx card is holding you back. i would probably go with this card if i were you

http://www.newegg.com/Product/Product.aspx?Item=N82E168...