How to edit a

gpg --edit-key 97DFS8D7FS8DF79S8DF

Change how the primary key can be used

gpg> change-usage
Changing usage of the primary key.

Possible actions for a RSA key: Sign Certify Encrypt Authenticate
Current allowed actions: Sign Certify

   (S) Toggle the sign capability
   (E) Toggle the encrypt capability
   (A) Toggle the authenticate capability
   (Q) Finished

Update the expiry date

gpg > expire

backing up a gpg key of specific user

gpg --export --export-options backup --output ~/keyname_public.gpg  
gpg --export-secret-keys --export-options backup --output ~/keyname_private.gpg
gpg --export-ownertrust   > ~/keyname_trust.gpg 
gpg --export-ownertrust  > ~/keyname_trust.gpg