Are your trying to change just the pulley or the whole tensioner assembly? The pulley itself is about $20 new, while the tensioner assembly is about $75 for a new part.
No advice on tool types and sizes, but a reminder that the bolt that holds the pulley on the tensioner mount has a LH thread. That means you turn the pulley bolt clockwise to loosen it. Turn it the normal counterclockwise direction and it will not come off and may even strip the threads. If you are going to change the whole tensioner assembly, this isn't a concern.
If I remember correctly, the tensioner bolt is 19MM and the pulley is 18MM. The pulley is LEFT HAND threaded so to loosen it you turn the bolt to the RIGHT. It is much easier to remove the pulley bolt with the tensioner attached. Use a large breaker bar on a six point socket.