Merging two Paddocks or Fields into one.

Go to System setup and Select the Farms, Fields tab (or Farms, Paddocks tab) and select each old field or paddock you wish to merge and untick the Current checkbox and enter a Date Retired as below:

Then create new paddock or field (which will represent the newly merged paddock or field) as normal including drawing the new merged boundaries in the field or paddock map. 

If you want to keep the name you used for the original paddocks ("Fred's") as one of the names for the new sections ... Rename the old paddock to "Fred's Old" ... Use Tools / Paddocks / Edit