MEMBER TITLES:
1. Control Panel > Profile Settings > Member Titles
Edit the titles to whatever you want.
2. Check the box if you want to update existing users with those new titles.
That's all
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LANGUAGE FILES:
If you want to edit the language used for your entire site;
1. Control Panel > Languages > Language Editor TAB
2. Enter "Search String" text, such as "User". Click the "Go" button.
3. Edit the fields as you choose. Click the "Update Language File." button after each edit.
