I have decided that upgrading the harddrive on my old iMAC, doing it myself is not for the faint of heart. I might have to get a shop to do it.

it is certainly not for the faint of heart. Especially depending on what the model of the iMac is.

I'm not quite sure if upgrading from a HDD to a SSD is practical at all on the more "modern" ones you may be considering upgrading (late 2009 and later I think).

it might be less expensive to buy a new computer.

upgrading a hard drive on an iMac is something I wouldn't ever contemplate. Macs have a reputation for being closed systems and iMacs even more so.

especially the newer models. The harddrives and RAM are soldered in.

Apple Mac Upgrades - RAM, SSD Flash, External Drives and More have good videos guiding you on how to do it. A good SSD will give it new life.

my iMac is at 9 years now. So probably time for a new one anyways. Except Apple hasn't really made a new one in quite a few years.

that our newest iMac was 3 years old when we bought it, it is more than a 3 year old model now. And has been repaired twice already. Well "repaired". Last time was sent with a diagnostic report, and when it was returned that diagnostic report mostly was "not fixed".

I put an SSD in my 8 yr old MacBook and it really made a difference