To install a custom site template:

1. Login to your account: http://www.networksolutions.com. If you've forgotten your log-in information, please visit: https://www.networksolutions.com/manage-it/forget-login.jsp.
2. Click "My Products & Services" in the top navigation
3. Click "My SharePoint Package"
4. Select your SharePoint package (if you have more than one package, you can select the specific package on the SharePoint selection screen).
5. Click on the "Login to SharePoint" button and log into your SharePoint site with your main username and password.
6. Click on "Site Actions" near the right hand corner of your screen.
7. Click on "Site Settings".
8. Click on "Site Templates".
9. Click on "Upload".

You may upload your own custom .stp site template from there. You can then create subsites using this site template by going back to "Site Actions", "Site Settings", "Sites and Workspaces", "Create".

Under the "Custom" tab, you will see the site template that you uploaded.

Note: Custom templates can only be used on subsites, and not on your main site.