From Longman Dictionary of Contemporary Englishbrush up (on) something phrasal verbIMPROVEto practise and improve your skills or your knowledge of something that you learned in the past I must brush up on my French before I go to Paris. → brush→ See Verb table
Examples from the Corpus
brush up (on) • I have already said how little I knew about cancer, and I now began to brush up on it.• For the province's future Olympic hopefuls have been brushing up on skills both on and off the sports fields.• Public libraries frequently have computers that people can use to brush up on their skills.• The guide can be used an introduction to the hobby or as a means to brush up skills. 