Can I upgrade Snow Leopard to Lion via a USB drive?

Yes, you just need to have Lion downloaded from the App Store and use the Lion DiskMaker to create a bootable USB drive, then reboot with the [code]option[/code] key pressed and select it as the boot device. read more

After the formatting process is finished, go to the “Restore” tab to ‘restore’ the content of the installation disc into the USB drive. Select then drag and drop the source image (Snow Leopard) and the destination (the USB drive) from the left pane to the corresponding place. read more

There are three ways you can upgrade. Download the Installer from Apple directly to the computer that you want to install the new OS X onto. Take your computer into the nearest Apple Store and they will do the upgrade for you. Make a USB thumb drive installer that you can plug into your computer to upgrade it. read more