If you have apps already installed to your current microSD, I would take Guytronic's advice and move them back to the phone. As far as everything else, I just did this and it's simple.
1. Put OLD microSD in computer and copy all information over. (make sure you are viewing hidden files just to be sure)
2. Put NEW microSD in the phone to so that it can be formatted for the phone.
3. Put NEW microSD in the computer and move everything onto it.
That's it, this worked for everything including my maps that I had stored on the microSD and Xbox Music downloads.