Rake through the mulch and the leaves will start coming out. Often there is moisture underneath the mulch which is a contributing factor in these leaves getting stuck in mulch. You will probably have to use some force to get them loosened up.
Once you have raked them out reasonably, the next thing is to use a leaf blower to get the leaves out of the mulch altogether. This should do the job nicely as the leaves will start moving away and you should be able to get them away to a spot of your liking. Make a pile of these leaves. Generally making a pile next to a wall is easier and it is a good idea if a wall is nearby.
Collect the Leftovers
There will be some leaves that will be left behind even when the blower has been used. Wear garden gloves and remove these with the help of your hands. Add them to the pile and they will be ready to go once you take them out. Your mulch should be leaf free by now.
Once you have removed them from the mulch, make sure that you put them in a trash bag so that they do not fly back into the mulch or around the garden or lawn. Once they are bagged, they will not be escaping. Some people put the leaves in a wheel barrow and take them for disposal. It is not a bad idea but the wind can blow some of the leaves away.