I decided to upgrade a new Cisco AIR-LAP1142N-A-K9 from the factory lightweight image to an autonomous image so I can have a standalone AP in the event my WLC takes a dive. A buddy of mine asked me to post some instructions for him, so here it is. I completed this in just a few minutes, so this isn't a big deal. In my scenario, I pulled the 1142 straight out of the box and plugged the 1142 into a POE switch so DHCP to assign the 1142 an address so I could access it via my PC which is also my TFTP server for this exercise. I'm using PuTTY for serial access to the 1142 and SolarWinds TFTP Server.
1. Download your 1142 image from Cisco --- I chose c1140-k9w7-tar.124-21a.JY.tar
2. Copy your 1142 image to your TFTP folder and start your TFTP server
3. Hook up your console cable and open up PuTTY
4. Plug in your 1142 into your POE switch and ensure it'll get an IP
5. When it boots and your DHCP server gives it an IP address, you'll get a prompt (*your AP needs to get to your TFTP server)
Use PuTTY and enter in the commands in bold and modify the address of your TFTP server and image accordingly.