How and When Can I Transplant Roses?

It is easier to transplant them during their dormant cycle.... However, it can be done. First and foremost, WATER. You will lose a little root mass, so the plant will not be able to take up water as quickly as before. Drown the plant the day before you plan to move it. (overwatering is impossible here), you need it to be swimming, if the plant wilts during transplant it will be doomed. Prepare the new spot at this time and get it ready.

Try to keep as much top and root ball as possible. (If you need/want to reduce the plants size, keep the roots over the tops). Now transplant, then wait and let your plant decide how much of its top it can support now, (less roots, less support). If/when it starts to wilt from the tips, increase watering immediately and prune whatever didnt recover, remove the dead leaves and prune the dried cane tips to leaf bud. You may need to lightly prune after transplanting. You should have the new spot ready by now, you DO NOT want to let the roots be exposed for more than a few mins so place it immediately. Dont let the roots be exposed to the sun at all, cover with a damp burlap sack if necessary.
Now you want to wait til new growth starts before you restart fertilization. Fertilize lightly til next year. Roses need LOTS of water. So you should water at this time. If you see any wilting, water immediately. When you start to see new growth... they are out of the shock, and adjusting. (despite the myths, the old spot may be reused).... Heres the break down;

PREPARATION
Plan the new location
Prepare the new hole/bed
Arrange for some help and a wheelbarrow/transport for transplanting day
Hyper-water the plant day before
TRANSPLANTING DAY
Dig the rose with as big a root ball as you can manage
If the plant is physically too big to move, remove some top growth
Plant the rose in the new bed immediately and water copiously
RECOVERY (til new growth starts)
Continue hyper-watering
Hold off any fertilizing
Remove any withered/dead tips or leaves
Rest of Season
Fertilize lightly
Water more heavily than normal
Continue removing any withered/dead tips or leaves
Resume regular care after end of growing season

Enjoy your beautiful Roses.... I hope this helps!