Accessing North America charts in the TDS GTNXi is a very simple process.
From the Home screen of the GTNXi 750, select the charts page and type in a North America airport such as: KSLE.
The charts should appear as in the attached screenshot.
Unfortunately, currently there is no possibility to update or manually add other charts, but this is something that we may look in, sometime in the future.
Please let us know if you are having any problems.