I tihnk I may have had a problem like this before ( maybe not) I tihnk it was a bug but Per fixed it.
Apart from what Alvee says which works very good and all the time here is what I do ( in case it is slightly different what you do.) But if your first book is full then there is no point in having that opened to add more into.
But anyway blah blah blah.
Here is what should happen
When on a song and you click on the " change songbook" option the page will refresh but have a choice of all your songbooks, in my case I have 6 to choose from. You click in the wee circle option for what book you want, the page refreshes again and should show the book you chose.
If this is not happening then there is something wrong. Only Per could help. he can be contacted at admin@chordie.com
Tell him what you are trying to do, tell him what you are using, internet explorer/ firefox etc
hope this helps you
ken
ye get some that are cut out for the job and others just get by from pretending