The Global Code Change Program ( found at Tools > System Utilities > Admin Utilities) will change one code value to another across all the tables that use that field.  If you only wish to change certain values, then one of the other global change utilities might be more appropriate.

This program uses a comma separated file (csv) as an import with the following format:
     Table Name,Old Key Value,New Key Value

The first column, Table Name is the FIMS Code Table Name. Use the FIMS Tables and Fields list to find the proper table name.
The second and third columns are the Old and New Key Values.  Both the old and the new values must be present in the code table.  So if you are changing all aaa values to zzz, both aaa and zzz must be in the code table.  Once the modification is made, you can go to the code table and remove the now unused aaa value.

This tool changes all of the records for all of the tables associated with the code table from the old value to the new value.
For the above example Region, it will change all of the region codes in Application, AppHistory, Grants and Fund Distributions that are "Town" to "D1".

For an additional example, the staff code value can be found in many places including the Fund 1 tab as Staff, the Grant Application as Program Officer, the Donor record as Staff, etc.  This program will replace all instances of the staff code with the new value.  If you only want to change the value on specific records - like open applications or contact tickles, it is best to make the changes manually one at a time on the appropriate records.  It is possible less global changes can be made with the regular Global Change Program because that handles one table at a time and allows for limited filtering.