When you purchase Cisco with CAPWAP feature, such as Air-AP1815I-K-K9, Air-AP1832I-K-K9, Air-AP1852I-K-K9, Air-AP2802I-K-K9, or Air-AP3802E-K-K9 and wish to convert it to Mobility Express. First, you need to obtain the latest firmware from software.cisco.com.
After login into your AP console, enable it
#show version //to check your current version. eg AP Running Image : 18.104.22.168
#capwap ap ip 10.0.0.101 255.255.255.0 10.0.0.1 //Set an IP address to your CAPWAP AP
#show ip int br // to make sure your IP address is set
# ping 10.0.0.2 //Make sure your TFTP Server is reachable.
# ap-type mobility-express tftp://10.0.0.2/AIR-AP3800-K9-ME-8-5-103-0.tar //ME File we download
if you found any error, you might need to upgrade your CAPWAP version to the latest first. One of the possibility is your current version less than 8.3 and you will need to upgrade to CAPWAP 8.3 or higher:
#ap-type mobility-express tftp://10.0.0.2/ap3g3-k9w8-tar.153-3.JF.tar //Upgrade from CAPWAP 8.2 to 8.5
#show version // now to check your current version after upgrade. The version should be at AP Running Image : 22.214.171.124
# ap-type mobility-express tftp://10.0.0.2/AIR-AP3800-K9-ME-8-5-103-0.tar //run again this command to upgrade to ME
Note that with current Cisco Aironet 1800 Series, 2800 Series, 3800 Series, as long the SKU end with K9, it will be CAPWAP version (Light weight AP or Controller Based AP), it need a controller, not able to stand alone.
If you looking for standalone AP, or Mobility Express Version, do request SKU end with K9C, eg Air-AP1832I-K-K9C, it will come with mobility express firmware.