The GPX tracks are files stored in the directory AGPS-Tracker. This directory will not be destroyed if you uninstall AGPS-Tracker and is directly accessible by any other App that is used to manage files in your phone. Photos are in its subdirectory called AgpsTrackerPhoto.
To see or transfer these files the easiest method is to connect the phone with a usb cable to the PC. On the PC you should be able to see the phone as a memory device and immediately see the directory and manage the files.
Obviously with the same method you can transfer the GPX files to the new phone. But first you should run the AGPS-Tracker app that, in its first run, will recreate the right directories.