Delete calculated field Excel 2013 Pivot Tables

Select the field in the pivot table, right click, and use the remove option.

Or select the pivot table.
Go to formulas on the pivot settings tab.
Select the field in the name box at the top.
Then edit the formula, or use the delete button.

How do I remove it (customized formula) from the PivotTable Fields?

Not sure I understand what the problem is.

Above description explains how to delete or modify the formula field.

If you just don't want to see it in the pivot table, remove it like any other field in the pivot table.
In the field set up box, select it, hold down the left mouse button, drag it outside the box and drop it.
Or remove the mark in the field selection box at the top of the field set up box.
If you don't see the field selection, use the Fieldlist button on the ribbon.

thanks for hanging in here with me. in the image below what I am trying to do is remove from the Pivot Table Field the calculated field labeled Average Sales that I created. I've tried everything you suggested but I can't seem to get this removed from my PivotTable Field list.

thanks