How to change "Add new node" button label? I have created two content types "A" and "B".
I have included content type "B" in content type "A".
So when I am adding a content of type "A" that time it shows me a button "Add new node".
I want to change this label with another label.
Also when I click on this button it display form with fields of content type "B". This also shows a button with label "Create Node" and a title "ADD NEW NODE". I also want to replace with another string.
I have used form_alter() hook.

Can any one guide me how can do this?
I suggest you take a small form_alter sample module code and start changing in it. Pl also see this video.

You can also do it easily using String Overrides module.