In the direct editing section there are the appropriate commands, e.g. "elimina face", more more specific for your purposes, than now I do not remember why I do not have the software at hand.
to eliminate the unwanted lines between two contiguous faces you can also use a command that in itself is called "replace face", I remember there is an equivalent even in soloworks, but I do not remember the name.
with if I have to admit that this kind of operations is much easier.
