Merge two endnote libraries

Can someone let me know how to merge to EndNote libraries?

From En X3 help:

Merging Libraries

There are three ways to merge libraries: import one library into another, copy references from one library to another, or drag-and-drop.

Any time you add references to a library, the newly added references are assigned new record numbers in the order that they are added to the library. This means that a reference that was #23 in a smaller library, could become #600 in a larger library. As a result, you cannot use the larger, merged library to format papers that have citations with the older record numbers.

Note: Before merging libraries, it is a good idea to make a backup copy of the library into which you are transferring references.

Tor previous versions, see your  EndNote help manual.

Are you talking about Endnote Web (this forum) or Endnote?  

If Endnote, just to add,  if there are duplicates, importing one into the other is better, using the  “discard duplicates” settings, (unless you want to decide which of the duplicates you would rather keep, later.  than the other methods of combining two libraries).  I am not sure whether Endnote web works in the same way.