Complete reinstall of operating system on old machine

I have an old iMac with the specs below.
I want to install the most recent OS available for this machine.
I want erase all existing data and accounts on the machine.
I do not have admin access.
I have an apple id, not associated with this machine.

If Yosemite 10.10.5 is the most recent that can be installed on this machine, then I want to erase all existing data and accounts on the machine.

What can I do?

Available: 158.72 GB (158,723,710,976 bytes)
Capacity: 999.35 GB (999,345,127,424 bytes)
Mount Point: /
File System: Journaled HFS+
Writable: Yes
Ignore Ownership: No
BSD Name: disk0s2
Volume UUID: 94E5A9F7-B5AC-35BA-8B5C-D3973289C5F4
Physical Drive:
Media Name: ST31000528ASQ Media
Medium Type: Rotational
Protocol: SATA
Internal: Yes
Partition Map Type: GPT (GUID Partition Table)
S.M.A.R.T. Status: Verified

According to everyman.com, the latest version of macOS for your Mac is High Sierra. There is this previous Ask Different question regarding gaining Administrator access: I don't have administrator account on my mac. You should be able to get High Sierra from the Apple website How to get old versions of macOS. There is also this previous Ask Different question: How can I download an older version of OS X/macOS?. One option, for a clean install of High Sierra, would be to create a bootable installer, boot from the installer, erase the internal drive and install macOS.

Given the age of this machine, consider dropping in a SATA-based SSD rather than the spinning drive it likely still has. Doesn't have to be be new - I put a 64 GB SSD in a 2007 imac successfully.

This will give you a completely blank disk to start from, and it will be a virgin install by definition. Also, its a decent speed boost and also helps with virtual memory speed.

Later you can connect your old drive via a USB-SATA adapter and read in any files you still want, then format it.