Hi! Sounds like you are doing great! I assume the mulch is some type of shredded wood/bark material? Many things can be used as a mulch over your soil such as this or shredded leaves, straw, and even rocks can be a mulch - retaining moisture in the soil, helping avoid wind damage to the soil, reducing weeds, etc. No need to remove last year's mulch. As natural mulch breaks down, you can replenish as you need to in order to protect the soil and keep down weeds, usually having at least a couple of inches of mulch. It is good to keep the mulch from piling up directly on the trunks of your trees/shrubs - you can brush it off from the woody trunks with your hands. Normally i let my perennials show themselves in the spring before adding new mulch so they do not get buried. New plants can be added by pushing mulch aside, planting, and then pushing mulch back towards the plants. The best sources of mulch are free (tree trimmers, leaves, etc) so do not be afraid to ask for those!

Leave the mulch, and add more on top if it's getting thin