To have someone else install your Themes means giving away password information and access to your site best left to you alone. Very dangerous. Never know who you could trust...and on this forum.....everyone is a suspect......hee hee hee....
Okay, doing the Vincent Price evil laugh doesn't come over very well in type, but you get my drift. Everyone here is very trustworthy...except the one with Moose in his name.....ha ha! - see, it just doesn't work. I'll work on the laugh.
Macmanx is right, following the instructons. It's really easy. You just have to have FTP access to your site, which can be done in Windows (looks like using Windows Explorer, so it's familiar) or FTP software. Find the directory for themes, usually
wp-content/themes/ and upload the FOLDER that the theme is in there. Don't dump the files in the themes folder, give it its own folder.
Once it is on your web site, then go to the ADMIN for WordPress, click PRESENTATION and then select your theme. View your site and bingo, it looks different. That's it. Very simple stuff.
Good luck....and I promise I'll work on that evil laugh thing.