All you should need is a PC/laptop, crossover cable, an IOS image, and some TFTP server software. And there is a good chance you have all of that or can pull it together fairly easily.
WIRELESS TAR IOS UPGRADE:
Follow the steps below to reload the access point image using the CLI. When the access point begins to boot, you interrupt the boot process and use boot loader commands to load an image from a TFTP server to replace the image in the access point.
Step 1 Open the CLI using a Telnet session or a connection to the access point console port.
Step 2 Reboot the access point by removing power and reapplying power.
Step 3 Let the access point boot until it begins to inflate the image. When you see these lines on the CLI, press Esc:
If you do not press the spacebar to continue, the process eventually times out and the access point stops inflating the image. Repeat until done inflating the files.
Step 8 Enter the set BOOT command to designate the new image as the image that the access point uses when it reboots. The access point creates a directory for the image that has the same name as the image, and you must include the directory in the command. Your entry might look like this example:
ap: set BOOT flash:/c1200-k9w7-mx.123-2.JA2/c1200-k9w7-mx.123-2.JA2
Step 9 Enter the set command to check your bootloader entries.