Merge New Terrain with old terrain, with preference to new

EnzoTT

hi, 
so i have two DTM layers  of a landslip, one is taken before earthworks and covers a larger area, the other after earthworks but is a much narrower area with some gaps from trees etc. Unfortunatly the flights where not conducted by us  i dont have the original files so i cat go back and redo there trimming/ lidar class etc. 

 in order to create a nice overall DTM/DEM to import into my other software ( Leapfrog) I would like to merge the 2 layers, but where the layers overlap give priority to the new layer. 

Possible?

EnzoTT

UGH!
 Answer, just export them as anew layer. no fancy merging.. Sometimes don't overthink it and try the basics!