Your SPT GPS is not a USB memory stick. To get GPS files from the device, and to erase the device you will need to install Bridge on your computer.
Here's how you install Bridge:
- Download the installer here: Bridge Installer for Mac
- Open the installer (double click on it)
- Once the installer opens follow the instructions
- When the installer finishes you will need to restart you computer
- Open Bridge (it will be installed in your Applications folder)
You will now be able to use Bridge to download and remove data files from your SPT GPS. We've written a tutorial on how to use Bridge, this will teach you how to get data off your SPT GPS and how to remove old data from your SPT GPS.
You can also download and read the Bridge user manual.