I created a few groups with custom permissions and I was the owner but now I cannot edit the group setting as it says only the owners can do that. Also, I cannot ad or remove anyone to/from the group. There are a few other people with Full Control. How can I change the owner back to me?
You can edit group permissions and membership if you are a group owner. The group can also be set to allow members of the group to be able add/remove group members.
So depending on what you need to do, you can request to be re-assigned as group owner, or have someone that is the owner (or site collation admin) to change the settings of the group to allow members to manage the group.
Here is some powershell to change the group owner of an existing group from Need to change the owner of an existing SharePoint group using Powershell: