The native WordPress fields (Username, Email, First Name, Last Name, Password, Confirm Password, etc.) can’t be edited or deleted. If you want to change the labels for those fields, you can do so by using the translation file.
The Ultimate Membership Pro plugin is translation ready, meaning you can add an additional language file (even English) to your language set on WP.
All the text elements that are not available to be managed from within the UMP Dashboard (native fields labels, buttons, etc), can be handled via the Translation file, the plugin being fully translation ready.
To learn more, please head over to this link.