Leopard download iso

Hi. Newly registered account here.

This site / specific download was recommended to me after I posted a "help me" post on Reddit ( https://www.reddit.com/r/mac/comments/iesq2w/need_to_update_mac_os_x_105... ) asking how I can update my mid-2009 iMac with Mac OS X 10.5.8 Leopard installed. To be honest, I found it in the trash, but it works perfectly. Long story short (more details in background story on the Reddit post if interested), I need someone to provide me with baby steps / for dummies version on how to upgrade my iMac to 10.6 using the software available on this page. I've tried doing it myself but I can't get passed the download page.

PROBLEM:
I can't seem to unzip the file for download #1. I likely don't know enough / doing something wrong. I've spent maybe 20 cumulative hours trying to successfully update to 10.6.

MATERIALS:
Have a 32gb usb3.
Willing to buy a dual layer burnable DVD if I must.

WHY:
I'm a poor teacher. My two young songs are doing school online all year. I was able to offer my 13 year old son an old 27in. iMac bought for $60 on Craiglist (El Capitain). But that computer already had El Capitan installed. I want my 9 year old son to have the current iMac I'm trying to update (the one found in the trash). Need to update because OS X 10.5.8 does not allow for seemless access to Google Classroom, which my son uses on his Fire tablet everyday ( Initially, I was able to give him an old Dell Inspiron, but it just proved too slow).

Please help... I started this project during the summer, but had to undergo open heart surgery in September, so I've been unable to work on this till now, while my son is struggling to do all his work on the fire tablet.

Thanks in advance for help offered. ........ Sal