One of the Layers funcitonality improvements in AutoCAD 2014 is Merge Layers.
Merge Layers in AutoCAD
It is a new tool available on the right-click menu. Simply select the layers you want to be merged, right-click, and you’ll see the option Merge Selected Layers to… on the floating menu.
Click on Merge Selected Layers to… to open up the a dialog box where you can merge all selected layers. Select the target layer (the one that you want your other layers to be merged into), click OK, and all objects from all selected layers will be purged and those other layers removed from the drawing. These are quick, useful enhancements to the Layer Management tools.
Another option is to start the LAYMRG command from the Command Line or from the Ribbon menu (see screenshot below). First select those objects from the drawing area that you want to be merged, then select an object on target layer (and automatically delete the now empty layers).
Don’t miss out my other post about Layer improvements in AutoCAD 2014: Sorting order of numbered layers.