Edit a copy of a monster without modifying the original entry from Monsters Manual

Hello, I'd like to use a certain monster's basic stats from monster manual to create a new monster modifying the original stats and other stuff. I've tried to make a copy of the original monster and then edit the copy, but every change I make on it affect the original entry. Is there a way to make a stand alone copy and then edit it without changing the default stuff of a monster?

I think if you change the name of a Monster Character, you can drag a new copy of the Monster in from the Monster Manual. That said, what do you mean about your edits affecting the original entry, that shouldn't happen if you duplicate the Monster.   Or do you mean that you are changing stats and the original monster's abilities reference the new one? (The reference would be by name, so changing the name should fix that too.)

Ok, the mistake was that I've tried to change the name directly from the monster sheet (by pressing the edit cog and then edit the name field). Now I noticed that if I modify the name from the above window I can create a stand alone monster. 

Ah, Great!  The name in the monster sheet field should change that name, but doing it from the edit will certainly work.