Go to the Merit Templates section of your Admin Dashboard on the left side of the screen.
Click the Field tab on the top bar for the list of Global Fields
To edit Org-Created Fields, simply click the Edit button next to any Field. You can change the name of your field and the description, but not the Field Type.
Clicking on the Edit button next to any Org-Created Field will allow you to change certain aspects. You can change the name of your field, as well as the description, but you will not be able to change the Field Type.