How do I withdraw my loved one from a memory care facility?

Find the place where you want to move him. They can help arrange transport if you need it. Ask them how best to make the move.
Are you moving a lot of furniture as well?
I would tell them in person. Consult any contract that you have signed. There may be something there as to how to give notice and how much time is needed.
I would also explain why you are moving him. If this is a problem that has been on going and they have not addressed it or resolved issues then I am sure the move will not come as a surprise. However if you have not given them a chance to correct problems I would allow them to do so. It is difficult moving someone and if he has gotten used to the staff and the facility a move might set him back a bit.

Just moved my step-mother, we had to give a 30day notice in writing. Check your lease.

cdbanuelos, pull out the "Lease" and find the paragraph that mentions cancellation of the Lease. Every place has their own rules.