What do you mean migrate? 

 Migrate from an old npub for new one. 

 Maybe mark old one as old in your name and announce your new one with it. 

Add to bio too. Then just stop using it 

 Maybe send out a few notes here and there saying you moved, for those followers who missed it 

 I saw this method, but I think it's to much work: https://thebitcoinmanual.com/articles/what-is-nostr-key-migration/