If you just have a few, and don't mind being a bit fussy with them, you can
move them now. Use a spade to dig all around them, and lever them up with a
lot of dirt around them. The idea is to dig deeply and widely enough that
you disturb the roots as little as possible. Put them in their new spot
right away, and water them in.
If you have a lot of them to deal with, you can do them anytime after the
foliage browns and withers. You can use the withered foliage as a clue for
where to dig. You will inevitably spear a few of them despite your best
efforts....After you move them, you can water a bit to settle the earth in
around them, but no other supplemental watering is necessary for the rest of
the summer. Water in the fall, when root growth begins, if you don't have a
reasonable amount of rain.
That said, be aware that tulips are chancy endeavor; they don't return
reliably like daffodils and hyacinths. Some varieties are more perennial
than others, and a lot depends on your climate and weather, but I treat any
returning tulips as a bonus, not a given.
Zone 6, South-central PA
Click to see the full signature.