as you may noticed, in the RC version 126.96.36.199 you find in the install/contrib/ folder an other folder called upgrade_redirect
In this folder you find some files. You can edit the index.htm and replace the logo with your logo.
Then create in your forum root an new folder called _uc and put all the files in there, but not the .htaccess. You must copy the .htaccess file to your forum root, but please note that you have an copy of your current .htaccess file, so that if you are ready with upgrading, you replace it with your old one.
The .htaccess file in the upgrade_redirect folder may also need some changes in the url so that its working for your server. You can edit this file with an editor.
hopes this helps you...