Walk if you can but it doesn't do much good unless you watch what you're eating.
If you can't walk
without pain you could use a stationary cycle.
I bet if you loose some weight you will get to a point when you can start walking without pain.
That's exactly what happened to me. I've been walking daily for almost 4 years.
Some things that will happen to you >>>
* At some point you won't be able to sit comfortably on a plastic chair.
* I had to change the seat on my bicycle... because the big fat squishy one I put on there when I bought it 6 years ago, felt exactly that...
big fat and squishy.
* You'll have a big pile of clothes you'll probably never wear again.