Become more comfortable with distance training first. Follow the novice Higdon half-marathon training plan. It will require an appreciable increase in your weekly volume.
www.halhigdon.com/halfmarathon/novice.htm
Select a fall half and give it a try. (also: enter a few 10Ks throughout your buildup) From there assess whether you're willing to take the next step — a 26.2 race. Good luck!
