You can do both, either drain the water down and add fresh water, or if you want, remove the bromine dispensor and let the levels drift down. Dumping some water is the quickest, but the most work. Letting drift down is easy, but will take a while. Other than the bromine level, how old is the water, and have you medicated it with anything else?
folks using bromine, once they get thier method down, report very good results with water quality. I used it for a while and didn't care for the system and switched to Dichlor and post soaking dosage very close to what folks refer to as the "vermornters method". I also have a freeshwater oxinator and I've had great luck with my water quality.
I'm not a fan of the N2 mineral prodcts, but there are some folks here that will tell you they have great results and it enhances thier water. My advice is to wait on the Mineral sticks and focus on getting your primary sanitation method under control first. After getting it under control and living with the tub and the water for a few change outs, I'd say then invest the money in a mineral stick and you can decide for yourself if it's a benifit or not.
Good luck.