I would not do anything dramatic because your Maranta is overall quite healthy. The leaf spots do commonly occur on this plant if the light, water, humidity and temperatures are not close to perfect. That is hard to manage in the home environment.
Many folks overestimate indirect sunlight. Across the room from a sunny window doesn't cut it. Bright indirect means just beyond where the rays of the sun can fall directly on the leaves. As close to direct sunlight as possible.
Watering is the tricky part and there is no formula. You will have to experiment yourself following the guidelines above to get it in the right place. If your local tap water is at all on the hard side (lots of minerals in it), then switch to distilled or filtered water. BTW, misting really does not help raise the humidity for more than a few minutes each day, so it is largely a waste of time.
Fresh soil, repotting and fertilizer are not recommended for plants that not healthy and growing vigorously. None of those will prevent the brown edges, but they may cause more serious damage to the roots.
Trim off the brown edges and focus on proper light and water.