I used pay-per-booking at first and just monitored my rental velocity until it became clear that I was better off using a subscription. It's pretty simple math really... and it sounds like your rentals haven't picked up enough to worry about it yet. I think once you know you will clear at least 10 rentals a year, the math works out more or less in your favor to be on a subscription -- although I hear they are upping the subscription cost this year so do your own math on this one.
As for switching, it should be under "My Account" and then "Billing Preferences". If you are on pay per booking, that box *should* be a drop down and you should be able to select annual subscription. If not, try adding a credit card and see if it shows up once you have a cc on file.
Good luck mate. From what I have learned, your rentals will pick up (assuming you have the basics covered like good descriptions and photos) once you get a few reviews. For me, it was worth it to drop my price until I got my first three 5-star reviews. Then the rentals started flowing in and I raised my rates back up.
Unfortunately, you may have to call Customer Service to change your account from Pay Per Booking to an annual subscription. I was originally on an annual subscription and I remember that I had to call CS to switch to PPB. Several months ago I switched back from PPB to an annual subscription but I can't remember if I could do that on my dashboard or whether I had to call CS.
The annual subscription price is currently $499/year. The PPB fee is 5% of your rent and fees. The "break-even point" between PPB and an annual subscription is therefore rent and fees totaling $9,980 in a 12-month period.
First of all, welcome to the community boards. We are in Arizona, so do not have your situation. However, we went directly into subscription service when we joined. Didn't even know about the other plan. Somewhere I read the calculation to determine which works best for you. You might do a search on the discussion boards for that.