|Far too broad a question and insufficient information. Try Google for general tips.|
Here are a few that come to mind:
1. Install more RAM if you only have a small amount.
2. Install and Run CCleaner (free).
3. Defragment the hard disk.
4. Uninstall unwanted programs that run in the background.
5. Make sure you don't have more than one Anti-virus programs running all the time.
6. Check for viruses etc. Malwarebytes freebie can sometimes find and fix what others miss.
7. Consider using "Write caching" on the hard disk if it is not already set that way.
There are stacks more possibilities, maybe someone else will add to this list.
Always pop back and let us know the outcome - thanks