Just do it! Only you're stopping yourself becoming the person you want to be!
I've got to be responsible and tell you to check with your doctor first. Get them to advise you on a sensible weight loss, probably about 1lb a week. Doesn't sound much but it crept on slowly so the best way is to take if off slowly. It's working for me.
I'll talk more about goal setting soon.
Then get yourself a bike. Don't go mad but do spend some money as you will get the bug and start using it loads. Spending between £200 and £500 will get you a good bike, but get some advice.
Try and find a nice flat route, couple of miles is a nice distance to start with. Take it easy to start with, so that you keep going.
Record your time so that you can keep improving. There are loads of apps that do it for you, I've used Sports Tracker, but have changed to Strava just because a few friends use it.
Go for it, keep going and you will love it.
Let me know how you get on.