Salesforce: How to change field Label created by Managed Packages?

When you installed a managed package app into your Salesforce instance, you cannot edit the label of the fields. If you click Edit button, both Field Label and Field Name is disabled.

So, how to change the label? Here we go:

1. Navigate to Setup - Translation Workbench - Override
2. Select the right Package, Language, Setup Component = Custom Field, Object, and Aspect = Field Label
3. It will show all custom fields for that object
4. Double click in column 'Field Label Overwrite'
5. Press TAB to move to next editable field or SHIFT-TAB to go to the previous editable field. 
6. Click Save button and done.

View in object page layout, before:

After:

With the same approach, we also can do for the following components:

• Action
• Apex Sharing Reason
• Button and Link Label
• Custom Field
• Custom Report Type
• Lookup Filter
• Record Type
• Validation Error Message
• Web Tab
• Workflow Task

Note: you do NOT need to enable Translation Settings to do this change.

Reference: 

• Entering Overrides to Translations in Managed Packages
• Component Behavior in Packages