Yeah if your goal Is to retain muscle it's suggested that the cardio be low to moderate intensity for longer duration. Running would be too much. Hiit will work break it into shorter sessions but stepmill or incline walk for 45 min is probably preferred. If u don't care about the muscle then run...
21% is pretty high. I'd say focus on getting that down as a priority. I would say focus on protein and carbs keep fats mod to low. If you can keep your protein around 200-250g and your carbs closer to 300 you will lean up a bit and put on a few good pounds. At 21% right now I would say lean you...