The 4800 firmware is available here:
http://www.cisco.com/pcgi-bin/tablebuild.pl/aironet_4800_series_ap
It seems you have a later release than they have posted so i would recommend sticking with what you have. It is unlikely there will be any more firmware releases as the AP4800 is an EOL product.
Nick Howells
Head of Solutions Sales - Collaboration
STS (Structured Technology Services)
T: 0116 240 8820 | D: 0116 240 8832 | M: 07764 710396
E: nickh@sts-communications.com | W: www.sts-communications.com