$ gpg --edit-key <uid>gpg> trust
Please decide how far you trust this user to correctly verify other
users' keys (by looking at passports, checking fingerprints from
different sources, etc.)
1 = I don't know or won't say
2 = I do NOT trust
3 = I trust marginally
4 = I trust fully
5 = I trust ultimately
m = back to the main menu
Your decision? 5
Do you really want to set this key to ultimate trust? (y/N) y
Please note that the shown key validity is not necessarily correct
unless you restart the program.
gpg> quit