Hi @katmurphy13, welcome to the Supernotes Community 
You can indeed rename all your tags at once using the Multi-Select prompt, by selecting all cards with a tag, removing it and adding a new tag – as Connor suggested above, so you can have more granular control over which cards / tags are changed.
Since notes can be shared it’s not as simple as just editing a tag (what happens if you’re a member of a read-only card, or if your friends didn’t want you to edit a certain tag). Multi-select gives you more control and visibility into your decision making.