brush up on

to improve one's knowledge of something

• You should brush up on your Spanish.
• He brushed up his English during his stay in London.
• He went to France to brush up on his speaking ability.
• Before going to work in Paris, I must brush up on my French.
• Before going to work in Paris, I have to brush up on my French.
• If you're going to go to France, you should brush up on your French.
• Before going to study in Paris, I have to brush up on my French.