To remove the cassette you will need a Park or Shimano lockring tool. Shimano is better. Then you need a method to keep the cassette body from moving as you loosen the lockring. The other tool required is the chain whip. As said before you can use some old chain to hold the cassette. Also, I have used a rag and my hand to keep the cassette from moving. This may or may not work because the range of allowable tork (lockring) is quite wide so it may be tight (requries the proper tool) or not really tight.