The mpl-token-metadata package requires you to use umi.

First you need to set up the umi framework: https://developers.metaplex.com/umi/getting-started#connecting-to-an-rpc

Metaplex has the docs on how to update tokens here:

https://developers.metaplex.com/token-metadata/update

In general, if this is a one time thing there are websites out there that you can use so that no code is required. One of those would be https://sol-tools.io/token-tools/token-management