There is some good videos on youtube showing how to use filezilla. My host ( hostgator ) also has some real good videos on ftp.

This is how I done it, first you will need to download filezilla. Next download the template you want to your computer. Then open filezilla . Everything on the left side of the screen is the stuff on your computer and everything on the right side of the page is what is online. Find the template ( looking on the left side of the filezilla page ) you downloaded and open it until you see the folder "includes" . Then I pointed my mouse at the includes file and clicked it, hold the mouse button and drag the includes folder over to the right side of the page and drop it in the folder that said "www"

Then go to your admin and click tools>template selector and you will see it.

Be careful dragging files, if you release the mouse at the wrong time it might take a while to find the file again.