You can try checking task manager to see if several programs are running at once. Sometimes when you install programs, they are automatically set to start up when you turn on the computer. If you don't use those programs that much, it can slow it down unnecessarily. You would have to go into each program's settings and disable that option, though.
If you have a lot of programs on your computer that you don't use, you can uninstall them. I wouldn't uninstall anything that came with your computer when you first got it, though - I'm talking about programs you have installed in the past that you don't use anymore.
If you have an antivirus installed on your computer, it can scan for malware and viruses, as well as optimize and clean up leftover files on your computer. If none of this is helping, you can always bring your computer to a repair service like Geek Squad. They'll charge you to check in and service your computer, but they may be able to clean up and speed it up, or get to the root of your problem.