Like ur dick aint small enough? :P Instead of stereoids, u can read up on how to naturally increase the level of testosteron in your body. There's a lot of discussion on wherether it's true or not, but many foods are rumoured to work positively on this.
Also, doing a full-body workout instead of one muscle group at the time will increase this. There's types of ginseng that increases testosterone too, but there's a high chance it tastes too bad to drink..
And of course there's a lot of sport supplements that advertise for increasing testosterone.. but i wouldn't buy any of that unless you find proper research that proves it.