Clean Boot
Disabling background apps that cause problems will help improve the performance of your game. Performing a clean Startup will help determine if there are specific background apps that are causing problems.
Check out this Microsoft article: How to Perform a Clean Boot in Windows.
Closing programs that require bandwidth, like chat clients, streaming services, or web browsers, will help even more. Programs running in the background may cause your game to play choppy or cause other performance issues.
If this did not help solve the issue try the next step in our troubleshooting: How do I check my drive for errors to solve Fortnite issues?