T-Mobile 535 - Manual (Page 17)

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Press Finish.
Step 4
New APN will be saved.
Press Close.
Note: Considering the limitations inherent in some Windows versions, the
new APN will be available for newly installed devices only. Should you
require such APN for previously installed devices, it is necessary to remove
the device and add it again in order to set the new APN (see Section 9).
Remove APN
Follow the next steps:
Step 1
Press the button with the key symbol in the main window.
Select Modify connection properties and press Next.