all of the sudden warlight become slower and slower

Close and reopen the app/browser that you are running WL on.
You could also restart the device you play WL on.
Close apps that you're not using.
Log users off the computer while you're using the computer.
To further increase performance, perform an anti-virus and anti-spyware scans and remove the viruses and or spyware.
Uninstall programs that you don't need.
Delete files you don't need.
You can also clean your disk. Consult Google if you don't know how to do this.
You could also defragment your disk. Consult Google if you don't know how to do this.
If none of the above speed up WL, your network connection is slow so upgrade your broadband package and or tell people who are using the same network as you to not use the network you want to use when you play WL.