To extend the grade boundaries on a post please follow the below steps:
Click Admin then click Post Setup.
Search and find the required post.
Go into the Post details screen then click Edit pay details.
Within Pay Details you can change the grades attached to the post if you amend the Grade lower and Grade upper fields.
Click Save.
📌Note: When you have changed the lower or upper grades, the lower and upper pay scale fields can be changed to include the pay scales from the newly selected grade.