Work on technique first, as it sounds like you need to do this.
Change levels, get underneath him, and lift with your legs. Be explosive (after you learn the technique that is) and during the penetration step try to step through them. The best thing for you to do is to find a wrestler where you live and have him teach you in person, its not something you can learn reading about. And keep practicing it too. It's not something you will be comfortable with overnight.
Also try asking this in the grappling form.