brush up
 brush up [  phrasal verb  ]
  brush up or brush up (something) : to improve your skill at (something) or increase your knowledge of (something)
   My Spanish is very rusty. I need to brush up before I go on my vacation to Mexico.
   I need to brush up my Spanish.
   — often + on
   I need to brush up on my Spanish.
  
 • • •
 Main Entry: brush