OK: I'm going to assume that you are riding on pavement and sometimes in the rain.
First, ditch the knobby tires; they have poor traction on anything but mud or loose gravel. Slick tires provide more surface area and therefore better grip to the road. High-pressure slick 1.5" tires will roll a lot faster as well.
Second, upgrade your V-brakes and pads. It looks like you have cheap stamped-steel V-brakes found on department-store bikes. Inexpensive Shimano V's are worlds better, and have better stock pads.
If you want a better all-round bike, also get rid of the suspension fork, which unless your commute involves travel over head-sized rocks, is a heavy and unnecessary impediment. It adds 2 pounds of useless weight, saps your pedaling energy due to suspension bob, and has less precise steering/handling than a rigid fork.
26" wheels are fine; 27.5" is dead, and 29" wheels and tires are heavy.