If you are an Account Owner you can update both Administrator and Budget permissions.
If you are an Administrator, you can only update Administrator permissions.
To do this, simply:
Click on your 'Organisation' icon on the blue left-hand navigation bar.
Find the person in the list whose permissions you wish to update and click on the 3 ellipses on the right-hand side.
Select Permissions from the drop down menu.
In the popup, move the toggle to grant Administrator or Budget permissions.
You can also bulk grant permissions. From your Organisation page:
Select all those you wish to grant permissions by clicking the box to the left of their name.
Click the Bulk Actions button on the top right of the page and select Permissions from the drop down menu.
In the popup, move the toggle to grant Administrator or Budget permissions.
Note: Click here for more information about permissions.