HD Question

I am getting ready to move in a few months.
I used to be a Dish Network customer, till my apartments made me take it down after a year. I can still access my account online.
I have the Dish 500 pro but no longer have the boxes.
Can I buy a dish 300 and use it for HD.
Can I convert the Dish 500 in any way. I kept the Sp34 switch
If I buy from Dish, is this a lease or is everything mine.
I want to own my own equipment, if not I will buy it off E-bay

Thanks for any help.