Hello Dabrowski, Welcome to the ACT! Online Community. There is a way that you can edit the contents of a single field for multiple contacts. You would perform a lookup of the contacts whose field value you would like to change, then go to Edit > Replace Field to change to value of that field for the contacts in your lookup. You can also use Swap or Copy as well under the Edit menu.
Note: Effective 6/1/13, Sage no longers provides support for the Act! software. This is now provided by Swiftpage.