Expiration date will change to January 2021 and you will need to achieve 300 points before that date to renew. If you want to upgrade to gold, then you need to achieve 600 points by January 2021, but again whichever month you upgrade will be your new 12 month period.

Edit: as you are already silver, reaching 300 points in January won’t change your membership year. You can either try to get a total of 600 (ie additional 300) points by august 2020, to upgrade to Gold, or just have your silver tier renew in august.