Each site on your account is independent from other sites, and thus each file should be uploaded for each site separately

1. Log in to your account.
2. Click My Sites and the word Manage for the site you want to work on.
3. Click Files Management.
4. Click Browse - this will now let you select the file from your own computer.
5. Once you have selected the correct file, click Upload.

The file will now be uploaded to your File Management and you will be able to see it under Links. You might want to click on the link to make sure that you have uploaded the correct file.

The link you receive is the one to use in the Front Page Layout when editing the layout of your site.