I am trying to close background running apps on my Xperia X10 how is it possible?

I was facing a few problems with my Xperia X10 (it was too slow, sometimes is was "burning") and a friend of mine told me that maybe there are many apps running in the background of my phone. He told I had to stop them and my phone would be okay.

I thanked him, but I didn't ask him how I do so... Could you guide me how to close background running apps?

Mazz is an easy process, go to the Settings and click on Apps then click on the tab "Running". There you will see the background running applications, click on those which you wish to close and select Stop.