Removing plaster and lath is a mess. Get some heavy drop cloths and protect your tub first. There are different ways to accomplish this task:
1. Use a sawsall to cut the wall into sections between the studs. then knock off what remains attached to the studs with your hammer.
2. Use your hammer to knock the plaster off the slats first. Clean up the plaster...then pull the slats off the studs. This is much easier than trying to strip everything at once, and clean up the plaster with the slats mixed in.