How to change a field label on a Managed Package field
Components of Managed Packages are not editable by standard methods (i.e. clicking Edit next to a field in Setup). This article will demonstrate how to update a field label using the Translation Workbench. Note this will change the field label, but not the field name/API name of the field.
In Setup, click Translation Workbench --> Override
In the override screen, select the Package that contains the field you want to relabel
Note: If you are using NPSP3, and you aren't sure which package a field is in, you can try Nonprofit Starter Pack, Contacts & Organizations, Households, Affiliations, Relationships, or Recurring Donations.
Select the Component that you want to relabel (in this case, Custom Field)
Note:you only have to select language if you are using multilingual features in Salesforce. Then you would want to set up different labels for different languages. Otherwise your organization default (in this case English) will automatically appear in that field.
Select the object where the field resides
Select Field Label
Note: you also have the ability to change the related list label on objects connected via lookup fields
