Cisco APs ending in C (i.e. AIR-AP3802I-B-K9C) come with Mobility Express by default. They can be converted to a Lightweight AP.
Boot the AP and connect to the console port.
Go through the initial configuration and ensure your Management interface can reach the default gateway.
(I’m not exactly sure why reach-ability to the default gateway is necessary, but I couldn’t get it to work otherwise.)
The AP will reboot after the initial configuration.
Log back into the AP
Go into AP Cisco Shell:
(Cisco Controller) > apciscoshell
Log back into the AP again
Go into enable mode:
(Cisco Controller) > en
Change to CAPWAP mode:
(Cisco Controller) > ap-type capwap
The AP will reboot one more time, then it will be in CAPWAP mode.