Go to the NEW_UPDATES sub-directory and use ``gdiff'' or ``xdiff'' to compare each file (one at a time) in OLD_UPDATES with the corresponding one in NEW_UPDATES. As an example, consider the file ``grids.F'' and use the command
gdiff OLD_UPDATES/grids.F grids.F
Within ``gdiff'', click the right mouse button to bring up the option menu. Select PICK RIGHT to mark all changes from ``grids.F'' in NEW_UPDATES. Then scroll through the code and use the left mouse button to mark each local change to be taken from ``grids.F'' in OLD_UPDATES. In the event that part of a local change from OLD_UPDATES overlaps a change from NEW_UPDATES, an editor can be used afterwards to make the resulting code as intended. With ``xdiff'', individual lines from overlapping changes can be selected from each file which makes the use of an editor unnecessary. When done, use the right mouse button to select WRITE FILE. The correct filename and path ``NEW_UPDATES/grids.F'' should appear as the default. After clicking on the OK button, this new file containing all marked changes merged together will replace the existing file in NEW_UPDATES.
When finished, all local changes will have been transferred to the files in NEW_UPDATES. As a check, use ``gdiff'' to compare routines in NEW_UPDATES to the ones in the new MOM_3 directory. Only local changes should show up. As newer releases of MOM become available, the above strategy for upgrading is strongly recommended. This method has been in use at GFDL over the past year to incorporate new changes into the development version of MOM as well as to upgrade researchers from older versions to the development version.