Steps I took for upgrading ( using webhost4life):
1. Make a back up of db;
2. Make a copy of the entire website folder and upload the DotNetNuke Upgrade files by doing the followings:
a) Create a new root folder on webhost4life;
b) Zip the current working web folder (the folder which has the entire dnn installation);
c) Unzip the zipped folder into the newly created root folder;
d) Upload the dnn upgrade files to the server's newly created folder.
3. Point the site directory to the newly created folder.
That's it. This way you don't need to change any keys or anything on web.config file. And if there is anything goes wrong, you can change the path to the old folder immediately.
Remove all the unnecessary modules before the process. Make sure module versions would work with the new dnn installation.