I have an old PGP using old GnuPG algorithm defaults. According to Best encryption and signing algorithm for GnuPG: RSA/RSA or DSA/Elgamal?, those algorithm settings are no longer sufficient, so I want to move my PGP key to more secure algorithm settings. What is the best way to do that? Do I have to revoke my key and create an entirely new key?
There is no way to "upgrade" an OpenPGP key. You will have to create a new one, and you will loose your reputation in the web of trust.
Some people I met decided to stick with a RSA 1024 primary key, but use stronger subkeys instead (which is easily possible without losing your reputation in the web of trust), which comes with secure day-to-day use (for encryption/signing documents with your subkeys), but might enable attackers to add and revoke certifications, subkeys and UIDs.