If you cannot pull this up by hand, try working a small hand trowel or pry bar under the bottom edge and levering it out. Sometimes the edging is anchored with stakes, so be sure to remove them first.
Follow along the existing edge, if applicable, or the line you have marked out with the hose or other material. Cut down 4-6 inches into the soil. Hold the tool firmly, push it into the sod, then use a sawing motion to avoid any stones in the soil. Cut all the way down along the line marking where you want the edge to be.
You can use a weed whacker or a gas powered edger instead.
If the flower bed is not overgrown, consider installing weed fabric around the plant before adding mulch.
