Updating device name requires 'import settings'. This is done in 2 ways:
Method 1 (individual device update):
Go to APs/Devices
select Device that needs updating
Go to that device's 'manage' page
Use the 'import settings' option
Method 2 (bulk device update):
Go to APs/Devices
Display all entries
select the 'modify devices' above the device list table (this should expand table to have checkboxes next to devices)
select all the devices you'd like to have 'device name' field updated
choose 'import settings' (it's halfway on the list of bulk options below the device list table)