I don't know how many times I've tried to use Cisco's free upgrade tool and had something go wrong, but it was too many to bother trying again. As with most things Cisco, CLI is my favorite way to do it. I did a little research and found a command that saved me all the frustration of the Upgrade Tool.
Here's all you need to totally bypass the Upgrade Tool and do it yourself:
1. Download Tftpd32/64: Link
2. Start Tftpd32/64
3. Change your current directory to the directory to the directory that contains your LightWeight image file
4. Log in to your AP (while its attach to a network your PC can access)
5. Input this command:
Ap#archive download-sw /leave-old-sw tftp://(tftpserver IP)/imagename
6. Allow AP to download image from your PC.
7. Reload AP
8. Sigh (you're done)
If you really want the link to the UpgradeTool here it is: Link
