I believe SecretSquirrel was trying to say that if you have, or intend to pland any plants, shrubs, or other vegetation in the beds, then you should not really have more than 2-3" of mulch on top of the soil.
To raise your beds, I would either remove the mulch and put down soil. You can order it by the truck load depending on how much you need. Or, you could leave the mulch there and add soil to it, working the two together, to reach your desired height. Then top off with fresh mulch. Mixing mulch and soil together is actually a good way to increase aeration of the soil, and since the mulch is organic it will eventually break down completely into the soil.
Once you have reached the desired height by adding soil, top off with fresh mulch at a thickness of 2-3" to allow for proper water penetration and retention. If you are going to be adding any plants or other vegetation, it is much easier to do the planting before
topping off with mulch