If you are looking to simply end the lease, there is no technical requirement for you to notify your tenant. However, I would certainly recommend you contacting the tenant to let him/her know your intentions. In your case, the plan to switch to a month-to-month lease definitely requires communication and the execution of a new rental agreement.
I would suggest sending a written letter (physical and email) informing the tenant of your intent to let the lease expire. You should do this about 2-3 months out. This letter should also include the intent to switch over to a month to month lease. After your tenant understands your plan, you should prepare a month to month rental agreement and make arrangements to sign.
In general, more communication is certainly better than less. This ensures that you have covered your legal obligation to the tenant. Put yourself in your tenant's shoes...you would definitely want your landlord to be open with you regarding his plans for your tenancy.
Let me know if you have any specific questions!
I completely agree with @Nick Baldor that you should let the tenant know your intentions asap. However, you may not need a new lease agreement for the month-to-month. Many leases, including the Board of Realtors lease, have language that says the agreement automatically reverts to a month-to-month agreement one the initial time period is concluded.
Then again, having a new agreement between you and the tenant would keep the situation very clear, but it may might be redundant...