Edit a drop down list contents

Hello,
I am using MS Office 2010 and Ive got a drop down list I need to edit. The list contents are in a named range called "Ack letters?" on a sheet called Drop-down lists in cells as follows

J1 Ack letters?
J2
J3 Yes
J4 No
J5 NA

J2 is a blank cell

The drop down is on sheet "Day 1" in cell H58. I've already edited the list by adding NA in cell J5 but I can't seem to get the actual drop down to recognize the change in the named range. How do I get the drop down list to recognize the change? Thanks for your help

Thank you for the quick reply. I felt like I was missing something so I went to the Data/Data Tools/Data Validation section and it allowed me to add cell J5 to the list of drop down options. It works fine now