Upgrading to virtualbox 4.3 using synaptic

[Jim Byrnes]

I am running virtualbox 4.2.18 on 12.04 that was installed with 
Synaptic. I see that virtualbox 4.3 is in Synaptic now.  If I choose to 
install 4.3 what will happen? Will it upgrade 4.2 to 4.3, over write 4.2 
or install in addition to 4.2?

Also I just noticed on my new install of 13.10 virtualbox is at version 
4.2.16. I would have thought 4.3 would show up there before on 12.04.

Regards,  Jim