My 5 year old water heater would make a loud crackling sound like firecrackers after we have a hot shower. I read that we should lower the temperature (not too hot). I've done that and I've drained the water heater. I have 2 questions:

1. How much water do I drain, is it until the water turns clear or do I have to drain it all the way since I'm sure the minerals are at the bottom of the water heater?

2. I read that sometimes changing the water heater temperature and pressure valve (located on the top or side) would do the trick. Can I do this on my own w/o scalding myself? Its on top so I think its OK but do I need to fully drain all the water out before doing this?

Thank you in advance for any tips!