This problem is a common one and is a good one to be asked, so well done. Carl is right in his comment, though I've heard the phrase "perfect practice makes perfect" instead; the meaning is still the same. If you are practicing for an hour, but practicing incorrectly or with poor technique, you're only wasting time.
If you want to play fast, you have to learn how to play slow.
Yes, this is zen, and thinking this way will enrich your practicing sessions. You become tense when you play fast because you lack the technical facility to perform the motion in a relaxed fashion. Thus, your body does the logical thing and uses your muscles / brute strength to compensate for underdeveloped technique. The result is unnecessary strain that not only tires you out but also causes health problems further down the road - and that's no good.
My first recommendation for you would be to begin taking lessons if possible / if you can afford it. If you can't, I strongly recommend purchasing a beginning percussion book and learning to read music (using the power of the internet!) if you aren't already familiar with percussion notation.
Next I would recommend that you begin learning rudiments - paradiddles, flams, single-stroke rolls, etc etc. I believe there are 32 standard rudiments, but don't quote me. A percussion method book will very likely have a list of the rudiments in the back of the book.
I would practice your rudiments *every single day beginning very, very, slowly and then very gradually speeding up (over the course of 2-3 minutes) to a point that is the fastest you can play without becoming tense (
Note: this will not be the fastest you've ever played, remember that.) Practice with a metronome and use that as your guide. Write down your highest bpm for each rudiment every day. Do not try to push to a higher bpm - merely allow higher bpm's to be reached when they are ready.
Over time (several months) you should develop enough technique to be able to play most anything relatively comfortably - especially with diligent, thoughtful, and meaningfully honest practice sessions.
Granted, practicing is an art form in itself and I've glossed over a lot, but the suggestions above should be enough to get the ball rolling.
The key always - always is to be patient, take your time, and enjoy the process.