assuming your goal is mainly to finish - you can probably do it on 3 runs a week. Keep 2 at your current 5k level, and find the time to get in 1 longer run a week - increase it slowly each week til u get up to 10 miles. With 3 runs a week and a long run of 10 miles, your body can complete a half marathon using the adrenaline you will get on race day. Run the first half carefully/slowly and hang on til the end. If you go out too fast in the race, you will pay for it at then end and for about a week afterwards - but you can finish!
If you want to get more serious - try for 6 days of running a week, and increasing your 5k runs to 5miles plus the longer 1. You would try to slowly get the long run to basically be up to 13 miles. This kind of training would start getting you into shooting for a time in a half marathon, rather than just hanging on.
good luck