Tenant need to sign rent increase letter?

Delivering my first rent increase letter. Original lease expired and it's now in month to month stage. Good tenants and I want to keep them. We have good communication and no issues. I've seen it both ways online, do I give them a later stating the new date and rent, or do I need them to sign a copy for me to keep with the original the lease? Just one house rental.

Thanks,

Bill