You start regedit.

cursor up/down, page up/down, or F3 to search, hitting enter to follow directories, until you reach the key.

Hit enter on the key. The values will be displayed.

Hit tab until you are on the key you want to edit.

Hit enter. A popup with the value will appear.

Type the new value, hit enter.

A much more painless process than I anticipated, honestly, and it refreshingly uses the same conventions that used to be used everywhere in windows.