knock down something
— phrasal verb with knock us/nɑk/verb
(DESTROY)
to destroy and remove a building, wall, or other structure:
The city is going to knock the old train station down and build a new library.
To knock down a system, practice, rule, etc. means to get rid of it:
He wants to use the WTO to knock down trade barriers.
(REDUCE)
to reduce the price, amount, or value of something:
He wanted $300 for the ring, but we got him to knock it down to $250.
The SEC knocked down their $1.5 billion penalty to $500,000.