Alexander,
If you have telnet/ssh access to the AP you can upgrade it using the "upgrade" command. TFTP example below:
upgrade tftp:///
FTP, HTTP, and SFTP transfer options are also available:
AP_B*#upgrade ?
FILE Location of firmware image
URL Location of firmware image
URLs: tftp://[:port]/path/file
ftp://:@[:port]/path/file
sftp://:@[:port]>/path/file
http://[:port]/path/file
cf:/path/file
usb:/path/file
