Generally, a written lease contains the agreed upon terms between the parties.
One party to a valid written lease is not permitted to unilaterally change those written terms.
If the written lease provides that the due date for rent is the 5th of the month, the landlord has no ability to change the date to the 2nd of the month on the current lease without the consent of the tenant.
This fact would be true until the lease term ends, at which time the landlord can draft a new lease with new terms and present it for a new signature by the tenant.
For an easy way to create a valid Rental Agreement, see Standard Legal’s Lease Agreement legal forms software page.