I build/repair inround vinyl liner pools, I would highly recommend not lowering the level of your water with wood walls. Actually lets find some info out first.
How old is the pool?
What did they use when building the pool to support the walls? wood or steel bracing? Is there a footing?
The reason I ask this is I have been on pool renovations on wood wall pools that are 20-30 years old. Once we lowered the water level down the walls caved in. Due to the previous installer using wood bracing. What happens is the wood bracing dry rots/decomposes.Once that happens the walls are solely supported by the water itself. Once you drain the water down the exterior pressure MAY cause the walls to coapse inward. I do not mean to scare you however I would call the contractor and speak with him, there is that possibility that you may need more than just your liner replaced

Thanks. He knows about the wood walls already. He replaced some of them with metal last year. I will wait to talk to him before draining.

It is about a 35 year old pool. I don't know what kind of bracing they used.