Computers start running slower as they grow short on space. One quick way to speed them up may be to get rid of apps that take up more space than they should, especially if you don't regularly use them.
To see how much space an app uses, navigate to Settings > System > Storage. Click on the drive you want to search (likely the local storage, "This PC"), and click Apps & games to see a list of apps installed on your machine and how much space they are taking up. You probably won't get rid of your browser, but you might find that a game you haven't played in years is some good dead weight to drop.
