Amending current lease for renewal

[James Marotto]

I recently bought a 2-unit that I'm occupying while renting out the other.  The current tenants (who "came with the property" and are great tenants) are due to renew their lease next month.  Can I simply amend the current lease that I inherited from the previous owner to update the landlord/tenant section and term (another year lease) or should I (or must I) create an entirely new lease for them?  This is a great forum and I've learned so much already...and look forward to learning more!  Thanks for any input anyone can provide.