Do I have to renew the trademark to keep the registration?

Yes.  Trademarks are granted for a period of time.  If you want to keep your trademark alive you need to renew it.  

The procedure is simple as the trademark office will not perform any substancial examination of the request.  They will just verify that you are still on time to request the renewal and that you have pay for it.

Most of the countries the trademark is valid for 10 years, except for Venezuela where they are just valid for 15 years.