Deleting data in picture field after making relational

Secondary file has a field ("Picture") that once held path to image file. Later I respecfied the field (now ":Picture") to get new path from primary database file. Do I need to clean out the original path data from the secondary file, and, if so, how? Deleting the field with all its data would cause an enormous amount of labor to fix the problems spawned in other related files. Since the database is already sluggish (and when converted to FMP8 it's too slow to use), I thought I should clean out as much junk as possible. Thanks for any comments.