Not able to delete alternate state names in Geographies

Summary:

When colleagues are trying to enter the address using Contact Info page. After entering zip code, there are 2 states in the drop down. One with abbreviated state name and other is full name. Upon checking Manage Geographies page, I could see State name has alternative names setup.

Users want to see only 1 field in drop down with abbreviated State Name.

Navigation: Setup and Maintenance > Search > Manage Geographies > Country Code: US > Select the Country name and click on the checkbox on Hierarchy Defined.
In Geography Type select State and search.

After selecting any State, there is a alternate state name. I am trying to delete the alternate name but the option is fade out.