Need more info.
What type of devices? Are you using AirWave to manage devices / push config to devices? If Aruba, are you using templates or Group based config?
Assuming that you're using Aruba devices:
1. Navigate to the group that has the controller
2. Go to Controller config tab
3. Expand WLANs
4. Select WLAN that requires update
5. Based on the type of encryption, you may see different options, but if using WPA2 -> enter the updated passphrase, and then retype it again
6. Save
7. Save and apply
The above steps will update the AMP profile for the WLAN. To push the update to the controller, you'd have to navigate to the controller's manage page, and then toggle for management (this requires that controller has read/write snmp string).