I thought dust seals should just slide out but these won't budge.Anyone know how to do it?

Large flat bladed screwdriver (or similar) under the seal is the only way. If they've been in for a while they'll probably be tight so work the screwdriver around the seal.
You'll want to put something on the lower fork leg to lever against. I've used the plastic pad spacer that came in Hayes brake calipers before, alternatively someone is selling the correct tool in the classifieds at the moment (£5, not me).
Be careful not to damage the washer between the dust and oil seal, make sure you get the screwdriver under the dust seal only.