How to set xampp server port NO?

I downloaded xampp my pc bt

start. When i try to start then show this massage "
Error: Apache shutdown unexpectedly. This may be due to a blocked port, missing dependencies, improper privileges, a crash, or a shutdown by another method.Press the Logs button to view error logs and check the Windows Event Viewer for more clues If you need more help, copy and post this entire log window on the forums