He paid always on time in 2018, until he renewed his lease with me this year. 

My question is: how do I go about notifying the tenant that I will not be renewing their lease? 

I have a one year lease that will renew in June but I had an opportunity come up that I don't really know how to handle.I have a detached garage that is apart of the lease agreement that gives the tenant full access to, but they rarely use.

@Mrinal Parashar, the existing lease stays in effect until renewal or termination.

If that's the case, then you need to wait until your lease is up and not renew or, if it's month to month, terminate the lease. 

I have one tenant that would like to renew her lease.

I do not purchase my own or renew the one the seller buys.

As the leases come up for renewal I am sending out notices that renewing tenants from previous management are required to show proof of renter's insurance within 30 days of their lease renewal.

So we paid water/sewage/trash for our tenants for 1 year and they didn’t want to move our so they renewed their lease which put them responsible for all utilities.

Once that first lease renewal date comes about you'll want to have your leases in place, along with your requirements.