Hi Reiner,
Upgrading to Pro version is very simple and straight. It should not hurt your blog. Following points might be helpful to you!
- If using FTP – than overwrite the contango folder with the newly purchased contango pro directory.
- If you want to upload via Admin Panel – than rename the old contango folder and upload your newly purchased theme.
- After activating the theme > Go to Appearance > Contango Options and “Save Changes” to verify everything is okay.
- Now the Contango Pro is ready!
Waiting for your response!