When you are login into your cPanel can not login andand it's shows "IP has Chanaged", there have easy way steps in your WHM panel,
-> Login into your WHM panel
-> Search and click "tweak Settings"
-> On security section search "Cookie IP validation"
-> By default "strict" change to "loose" option
-> Finally goes to last click on "Save".
Once clicked on save button you will following outputs,
Updating tweak settings...
Your changes have been saved.
Restarting cPanel daemons...done.
Updating your system to reflect any changes...
Updating Cookie IP validation from “strict” to “loose”.
Cookie IP validation was updated.