In Org without "Centralized User Management", there is no option to rename the group. Editing group was released in late Feb 2023 but unfortunately, this feature goes with "Centralized User Management" and we are still working on getting this rolled out to all our existing customers.

As described in the 13 March update on ID-6677 - Renaming groups after creation and in the public docs  Edit a group:
 

Editing groups names is currently a beta feature, here are some things to keep in mind:

• You can only edit group names if your organization has the centralized user management.
• You can't edit the name of a group if it's used within some Jira administration settings or if it has a restricted or protected name. Some group name changes could have an impact on your apps.
• If you edit a group name associated with a Jira Cloud automation rule, the rule will stop working.