If you need to remove a user or group from an existing group, you can do so from Partner Center.
Remove users or groups from existing groups
Go to Partner Center > Tasks > Users
Click > Edit group next to the group you wish to modify > click x to remove a user > click on Edit Group
To delete a Group, click> X delete group to remove the group
Note: If a user is part of a group in the Groups field, that user will continue to be part of the group you are editing. To ensure they are fully removed, you'll need to also remove them from any other listed groups they are a part of.