How do I change label forms after labels have been created

[Sarah]

I have a sheets of labels created in Avery form5266 and need to transfer the
text to Avery form 5366. How can I change the label form from one to another
without having to copy and paste each label?

 

[JoAnn Paules]

If it's already set up, there's going to be work involved. Ideally you
should have it set up for a mail merge so that you can pop that data into
any label format.

http://word.mvps.org/faqs/mailmerge/ConvertAdrsToDatafile.htm

or

http://www.gmayor.com/convert_labels_into_mail_merge.htm