Insert the SD2Vita adapter into the GameCard slot
Open VitaDeploy and go to "Miscellaneous"->"Format a storage device"
Press "Format target storage" and wait until it finishes
Reboot the console
Open VItaDeploy, make sure that the "uma0:" partition is visible
Go to the "ux0:" partition and select all the folders besides "SceIoTrash" (press SQUARE to select)
Press TRIANGLE and select "Copy"
Go to the "uma0:" partition, press TRIANGLE and then select "Paste"
Go to the Settings app and then navigate to "Devices"->"Storage Devices"
Set "ux0:" to SD2Vita and "uma0:" to Memory Card
Reboot the console, in System Settings it should now show the microSD size as the memory card size.