If you are only updating one field (the subtype field) of a particular table, then something like this would be all you need:
UPDATE DBO.SDE.TABLE1
SET SUBTYPE = 1
WHERE SUBTYPE = 2;
Running this statement in SQL Server Studio Manager as a user with write privileges on that table (or the 'sa' account) would change the values for the SUBTYPE field but no other fields. Let's say that you'd like to change all values that are currently '2' to become values of '1'. The statement above would accomplish this.
If your table is versioned, ensure that you have compressed to state 0 before doing something like this on the base table (i.e., DBO.SDE.TABLE1).