brush up

verb

1. To paint, or make clean or bright with a brush.

   “April 10, 1706, Alexander Pope, letter to William Wycherley You have commissioned me to paint your shop, and I have done my best to brush you up like your neighbours.”

2. To review; to improve an existing but rusty or underdeveloped skill.

   “I'll need to brush up (on) my Greek before my trip to Athens.”

   “How many will be rich enough to travel in style is difficult to know—but already 30% of the guests at the very expensive Mandarin Oriental in Hong Kong are from mainland China. Reception staff around the world had better start brushing up their Mandarin language skills.”

3. To beat up, annoy or insult (someone).