Q: How to free space on the start up disk Yosemite

I'm wondering how to free space on my start up disk after updating to Yosemite.

[Background info]

- I've had Sims 3 on my macbook air and when sims 4 came out, i had to install windows. It worked out eventually but then ran out of room, so i deleted windows, sims 4 and installed sims 3 again. Nothing would load.

I used Origin to try and play/install but now it won't work.

Whenever i try and do something, open an app or update something i get a warning that the start up disk is almost full.

I have completely given up!

I just want to see what "other'' is in the blue colour but nothing is simple.

I was to clear up heaps of disk space.

After you have updated to a new software, i.e Yosemite, do you have to delete the old software?

How can i see irrelevant items in my system that i can delete?

Any help would be great!

Here is my storage: