You may use the existing SD card from the head unit as long as the size of the current SD card is 32 GB. Older vehicle may have only 16 GB SD card which will not be enough space. 

If your existing SD card is 32 GB and because it will need to be formatted, we recommend to back-up the current files to your local hard drive first. Please follow this link on how to perform back-up

If you need to purchase a 32 GB SD card, please follow this link for the guidelines

Another option is to purchase the map & software update from