Hi, N.Borsell. I'm Robinson, and I’m happy to help you today.
You can try to open the Command Prompt as Administrator and start the Registry Editor from there.
1-Click on Start, search for Command Prompt
2-Right-click on that and select "Run as Administrator", you should be prompted to enter the administrator account and password
3-Once you are in the Command Prompt as Administrator you can try to open the Registry Editor by running the command regedit.