example: if u need update ur cIOS 249, then get installer cIOSX rev20b. load it from HBC choose IOS to Load (like 249, 250, 236, 36) then select ur IOS base (IOS 56) then Slot to be installed (249) and Internet or Wad installation.
cIOSX reb20 u can use some base IOS like 56, 57, 38,37... but 56 is recommended. if u need cIOS 250, then use base 38.
enjoy it