Replacing old values with new values at table level

Hi,

I have a issue like i have 40 custom tables,in that tables i have one field say FIELD6.only for this field i n eed to replace current values with new values.and in the custom tables this field name is defined as different names like in one table it is defined as ZFIELD6 and in other field ZZFIELD6 and so..on.i want a program to replace this field vaalues in all the custom tables.i have listed oldvalue and corresponding new value in a notepad,and uploaded these into one internal table as FIELD1 and FIELD2. And selected table entries from custom tables.and loop at custom table values internal table.but the problem is validating against upload file.any one give me the idea on this?

in the selection screen i have taken table name.