Transferring ownership is the only step required. (The new owner can change DNS settings once they have ownership of the domain.)
To do this, you will need to make sure the domain is unlocked and hasn’t been registered or transferred in the last 60 days, then get the domain’s transfer authorization code from the “Domains: Reg. Transfer” section of the DreamHost Panel and give that to the new owner. They will be able to use that at the new domain registrar to request a transfer.