If the car title has your name, then ‘AND/OR’ the second party’s name, you can change the title without their permission through the DMV.
However, if the title says only AND, you’ll need permission. In this case, get the other person to sign the title over to you. If they are not in the same area, you’ll need to mail it to them and wait for them to mail it back.
Once you have permission (if needed), go to your local DMV. Tell them that you need the title changed to only your name. If all the needed signatures are present, they will give you a new title and new tags.