brush up

Short definition from Wiktionary

Verb

1. 1
   To paint, or make clean or bright with a brush.
2. 2
   To review; to improve an existing but rusty or underdeveloped skill.
3. 3
   To beat up, annoy or insult (someone).

Noun

1. 1
   A slight correction or modification.
2. 2
   A review of a topic to be learned.