Partition to unlock memory card

First you have to download Mini Tool Partition Wizard Manager. You can download it HERE.

Insert your SD card to a card reader and open it on your computer.

Back up all your files to the computer because partitioning will wipe your data.

Open Mini Tool in your computer. Locate your SD card (be careful in choosing and make sure not to choose the drive of your computer)

Right click and choose Delete.

Right click on it again and choose Create New. Create FAT32 ; partition (This is where all your media files will go. Be sure to make it bigger than the 2nd part)

Select Create as: PRIMARY;
Next, create an ext2/ext3/ext4 partition (if you are on stock ROM, choose ext2).

This is where your apps will go. I suggest a value of 512Mb or 1Gb would be big enough but if you insist you can go as high as 2Gb.

Select Create As: PRIMARY (make sure that it is both set to primary because it will not work if it is not set to primary)

Click the Apply button on the top left corner and for it to finish the process. Done