I have lubuntu 11.10 installed on Acer Revo 3610

I have always used windows and have recently changed my media PC to Lubuntu. All I want to do at the moment is search for all teh files on my PC with a certain file extension and delete them, a trivial thing to do in Windows.
So far Ive had to download & install Cat Fish and so now I can search for them and find them all, but once it has completed the search I cant do a select all and delete. I can't do anything useful with the files once I have found them at all.

How do I delete all these files?