If you browse to Setup>Procedure Codes> Procedure Codes, select the procedure code you wish to update the fee for, then select the Fee Schedule Tab.
This will show you all of the fee schedules that that procedure code currently has a fee set for. If you select Edit Fee Schedule, you can then update the fee for that procedure code on each fee schedule the previous fee was set up on.
Note: If the fee was not entered on a specific fee schedule prior to updating it, that fee schedule will not appear on the list of fee schedules and you will need to add the fee by going to Setup>Fee Schedules>Fee Schedule Setup and editing that specific fee schedule. Once a fee has been assigned to that specific fee schedule for the specific code, it will show up on the Fee Schedule Tab under Setup>Procedure Codes>Procedure Codes for that code.