"About AirPort Base Station and Time Capsule Firmware Update 7.6.1
This update is for all 802.11n AirPort Express, 802.11n AirPort Extreme and Time Capsule models. It fixes an issue with wireless performance and provides support for remote access to an AirPort disk or a Time Capsule hard drive with an iCloud account.

For detailed information on AirPort base station and Time Capsule firmware updates, including instructions how to install the update, please visit:
All about Time Capsule, AirPort Extreme, and AirPort Express base station firmware updates
It is recommended that AirPort Utility 5.5.3 or later be installed before updating to Firmware version 7.6.1. iCloud setup requires AirPort Utility 6.0 and Mac OS X Lion v10.7.2 or later."

I updated a 3rd gen 802.11N (not latest model) AE base with this update under 10.5.8 w/Airport Util 5.5.3. (Seems ok so far and all settings were retained.)
  

"About AirPort Utility 6.0 for Mac OS X Lion
Use AirPort Utility to set up and manage your Wi-Fi network and AirPort base stations, including AirPort Express, AirPort Extreme, and Time Capsule.
    See a graphical overview of your Wi-Fi network and devices. Change base station and network settings, or manage advanced features such as security modes, wireless channels, and more...

System requirements: Mac OS X Lion 10.7.2"

FYI on v6.0 Missing Features: I'm not running Lion on anything and haven't used v6, but several readers sent notes that v6.0 is missing many features of previous versions including settings for Transmit Power, iPV6, Time Server, Multicast Rate, MAC Address Access Control and more.
(Here's the download page for the previous AirPort Utility 5.5.3. I don't use Lion so not sure if there's any issues with it. But also see notes on v5.6 below.)
  

"About AirPort Utility 5.6 for Mac OS X Lion

• Resolves an issue with using network passwords stored in the Keychain
• Works with AirPort Express 802.11g and AirPort Extreme 802.11g base stations

Addtional (sic) Information:
AirPort Base Station: How to set up and configure an 802.11g AirPort Extreme Base Station or AirPort Express in OS X Lion"

Update: Here's notes from a reader that installed v6.0 only to find it missing so many previous features/settings he regretted it. I wrote to ask if v5.6 worked OK with 802.11N bases (w/all settings, dual N band support, etc) - he replied:

" Hi Mike, Thanks for the updates. v5.6 on Lion looks pretty much identical to the older version. All the previous setting are available including the settings for 2.4 and 5Ghz.

One note to users who wish to use TM. (Time Machine, to restore the prev 5.5.3 version.) It won't allow you to roll back to the previous version if 6.0 is installed in the utilities folder. You have to restore and save to a new location.
-Phil"

I had mentioned TM in a mail to Phil (I was thinking delete v6.0 one then use TM to restore prev version) but also included a download link to 5.5.3. (Linked in v6.0 post above.)
  

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