How to Format an SD Card to a Smaller Size
Windows allows you to format removable and non-removable disks using the built in disk management console. With the disk management console, you also have the option to create partitions and shrink the file allocation size of disk, such as that of an SD card. Effectively reformatting and shrinking the file allocation size of an SD card is a relatively easy process, but, as with any disk formatting, you will loose all data on the disk when you format your SD card.
Plug the SD card into a card reader on your computer. Ensure that the computer recognizes the disk by clicking on "Start," selecting "Computer" and locating the SD card in the list of "Removable Devices." Close the window.
Click on "Start" and select "Run." Input "dskmgt.msc" and press "Enter." This opens Windows disk management.
Locate the SD card in the list of disks. Right-click the SD card and select "Format."
Click "Yes" confirming that you want to format the disk. Note that formatting a disk erases any data saved on the disk.
Input a name for the disk into the "Volume Label" field. This is optional.
Click the drop-down menu and select "FAT32" as the "File System" type.
Click the "Allocation Unit Size" drop-down menu. Choose a disk size smaller than the capacity of the SD card.
Place a check-mark next to "Perform Quick Format" and click "OK."