How to partition SD card on Android 4.1.1 using Linux?
Is this an external SD card?  If so, you can simply remove it from the SD card slot, and use either an SD card reader on the laptop, which may be built in, or you can get a cheap adapter that takes an SD card, and acts like a USB drive.  I've seen them on Amazon for as little as $2.25 including shipping, or nicer ones for $5 - $10.  Search for "sd card reader" to see.

Then, you can use gparted to partition it.  Just make sure to use the correct filesystem(s).