Follow the instructions in the Pre-Built Images section here to update your Gumstix COM with the latest software and the most recently tested, stable images.
Instructions to Update the Nand Image on your Overo COM
To update the u-boot, Linux kernel and root file system images in NAND on your Overo COM, start with a bootable microSD card and follow the instructions in this·Write Images to FLASH article. If you need to create your own bootable microSD card, follow these instructions to Create a bootable microSD cardarticle.
You can also use these images to boot from NAND When writing to NAND, keep in mind the size limitations of the NAND roofs partition. In particular you will need to use omap3-desktop-nand-image rather than omap3-desktop-image.
Note, if you just want to add some more software to your current image, check out our tutorial on the opkg package manager instead.