Once the tops die back, you can dig them up.

You could always lift the tulip bulbs, together with their roots and soil in one piece and replant in an empty spot in the garden. If there is plenty of greenery left, a little feed with tomato fertiliser and let them die down naturally.

I would just leave them were they are until they completely die back. If you want to feed them, fine. Lifting them sooner may compromise next year blooms.

As they're in pots, it's a lot easier to lift them - you can turn the pots out, carefully, and replant directly into the ground in a solid lump, so to speak, so you don't disturb the roots too much, then use fresh potting soil in the pots for your summer bedding.

in my big pots the tulips are about 6" deep and they stay in. I replace the top 4" of compost before adding the summer plants.

Sounds like a very sensible arrangement Sbg, saves a lot of work. Monty Don was knocking all his out of the pots in the latest program, as he wanted the nice pots for something else, the tulips he put in some plastic pots & left to die down.

I plant mine out. Some don't come back, some come back but with poor little flowers and just a few do well and spread.
If you need to keep them but have no room to plant them out I've found they do best in dry compost over the summer but that may depend on variety.