So, a new theme has been found on a random (and highly trusted) website for your new deployment of Magento 1.7.x.x. This is the fun part, finding the new theme.
The good news is that it’s not so hard to install that *.zip theme file you just downloaded from the random (and highly trusted) website.
Inside that *.zip theme file, after extracting it, you will find and app folder, and a skin folder.
Upload the New Magento Theme
If you browse using your ftp browser, you will see your Magento install also has two folders of the same app and skin name.
All you simply need to do is copy both of those folders (app & skin) into the root of your Magento install, and no files should be overwritten, but the new theme files should be written to the directory.
It would probably be worth your time to browse into both the folders while you have the new theme unzipped on your computer harddrive, as it’s easy to understand more from there.
To be sure you’ve installed the new theme, simply browse to the files that should be installed on your websites root.
The next step will also verify the files were installed properly, which is selecting the theme to be the current active theme for your Magento store!
Enable the New Magento Theme
To do this, from the backend dashboard (storename.com/admin), from the top menu browse to: system -> design. Select the store of choice that you’re wanting to change the theme on, and inside there, drop down the Custom Design option, and you should see the theme you just uploaded (or at least a name that somewhat resembles the theme you just uploaded, as most people label their themes with a funny name)!
Hope this helps customize your Magento store!