[Carl n Susan]

What size and ply tires are on there now? What is the year/month date of those tires (you don't want anything more then 4 years old). Given you have 6 tires I assume they are likely "E" or possibly "F" rated. "G' rated tires would be a definite overkill.

The are many places to buy tires. Online sites like Simpletire.com, TireRack.com or even Walmart will deliver directly to you. Big O, Discount Tire, aka Americas Tire, stores have reasonable prices on a variety of tires. Shop online to find what you want (stick to known brands with a good rep) and the price you want to pay.

For installation, you have two choices. Take the RV to a dealer and have them install the tires (even if you didn't buy from them) is the easiest route. Alternatively, jack up one side of the RV (you have the electric leveling system which probably isn't enough to lift, and hold the RV off the ground), put jack stands under the frame, and remove three wheels. You will want to take them to a tire dealer and have them mount and balance them (Americas Tire will do this for tires you bough elsewhere). When done with one side, repeat on the other. You don't want to try and demount/mount tires yourself.

Personally, I would find the tire I want. If it is at a tire shop, let them install. If they are shipped to me, take them and the RV to a tire shop who will install and balance for you. You are going to wind up a tire shop for mounting so the little additional cost to have them jack up the RV, remove and reinstall the wheels is minimal.