You can upgrade the firmware on your AirPort Base Station or Time Capsule as new firmware becomes available. If there’s new firmware available, you’ll be notified the next time you open AirPort Utility. Follow the onscreen instructions to download and install the new firmware.
You can also check for updates manually.
Open AirPort Utility, located in the Utilities folder in the Applications folder on a computer using Mac OS X, and in Start > All Programs > AirPort on a Windows computer.
Choose "Check for Updates" from the AirPort Utility menu.
Click Download to download all available firmware updates, or click Show Details to select specific firmware for the wirelss device you’re updating.
After the firmware is downloaded, click Update to install it on your device. If you’re updating more than one device, click Show Details to select the ones you want to update.
If you downloaded firmware but did not install it, you can do it later. Open AirPort Utility, select the device you want to update, and then click Manual Setup. Click Update on the Summary pane of AirPort settings to install the firmware.