Plants actually help lower your nitrate levels. You can add more plants or do more water changes. I would do a 20% water change every day until your levels are at or below 40 ppm (20 ppm is better). I don't recommend too many large water changes (50%) unless your fish are showing severe signs of stress. Large water changes will alter your water chemistry too quickly, could disrupt your bateria levels and cause your tank to cycle again, and 50% changes are just really stressful on the fish. Think about how you would feel if you were in a small room with the water level rising with your air space slowly but steadily decreasing. Your fish feel the same way when their environment starts to shrink.