Most will opt to keep all the history data with the original fields. Then create a new field name that represents the 2 fields combined. Then we can copy the field maps from the two field and edit the new field and paste addition. Here are the steps to follow:
Create a new field representing all the fields made into one Display the Farm Map that shows all these blocks Rubber band around all these fields or hold down on the Ctrl key and left click on desired maps. Right click and select Copy
Right click on the New Field name and select Edit boundaries. Right click on the mapping screen and select Paste Addition. If wanting to remove the gap or lines found between the two maps, click the Include polygon tool button. Left click in one corner of the first field boundary, drag across the gap and left click into the corner of the second field. Drag through the field boundary until getting to the opposite corner of same field and do another left click. Drag across the gap or line and then left click in that opposite corner of the first field. Right click and select Finish. The Goal is to actually trace around the gap or lines separating the two fields. Click Save and Close
Once you have the field boundary showing the two fields as one, the original fields can be retired (so they are hidden from the Tree View Listing. If or when wanting to view the history click the View Menu and select Show retired land area. Those retired fields will show with asterisks after the name. When finish reviewing the data they can be hidden again, by removing the check under the View Menu to Show retired land areas again.