How can I thicken a very complicated (poorly done) surface model so I can split it into parts?

I am a University student and have come across a massive hurdle that is stopping me progressing to the next part.

I require the attached surface model to be thickener slightly by a couple of (mm) so I can split the model into parts to create a lid and bottle type set up.

Could someone take a look and give any pointers please?

Thanks in advance.

SolidworksSurfacing