how do i backup my personal content/data (photos, videos, etc..) from my old sd card?

This is not supported in the Cricket store.  You can do this before or after your upgrade.

For backing up Photos/Videos: Plug a USB cable to your computer connected to your device. USB Mass Storage screen will appear, turn on USB Storage, go to My Computer, find Removable Disk, find DCIM, and drag pictures/videos to your computer.