Hi I have a field under tab 1. I now want to move that field to tab 2 but retaining all the existing data. Is this possible as I don't see any option? Thanks

If the backoffice UI doesn't let you do it, uSync probably will. Edit the uSync file for the doctype and import it. 🙂

If you open the property editor and go into re-order you should be able to drag and drop the property to the new tab. I have moved properties between tabs before and remember it being that easy and did not have problems with loosing data. I did not even have to change any code.