How to Cut and Join the parts?

Hi there,

I am Pretty new at SolidWorks ( actually CAD Softwares in General) and I have a Question which i cant solve even though i watched lots of YouTube Tutorials. I have to create a Mold for Plastic Injection Machine for my Part. The Problem is my part is way too big for the Mold. So i Need to cut it and make it shorter. In following Picture i tried to explain what i wanted to do with MS Paint .

So my Part has two Sections which are similar. My idea is cutting my part from the 1.line and then from the 2.line. After that i want to delete the section between 1.Line and 2.Line. In the end i want to Join the parts which are on the left side of the 1.line and Right side of the 2.Line so i can get a Shorter more compact Version of my Part.
The Idea Looks like quite simple but i couldnt managed to do it and i have 2 Questions .

1) Do you guys have a better Idea? ( I also uploaded the part if you guys wanna check it out)
2) If my idea is good enough how can i do it ? I watched some cutting tutorials in YouTube but dont know how to cut twice and join the rest parts.

Many Thanks in Advance