I have an IMAC 27inch late 2012 version and it is slow. What can be done to fix this?

My IMAC is very slow, the colour wheel can start when clicking on something and it can take several minutes to load. I am running MacOS Catalina.

What can I do to fix this, it is practically unusable.

Also, I want to update all my data to Icloud but I don't think this is happening correctly, as I can't locate files on my Macbook. I need help locating how backup is setup and possibly changing it.

Please help me, as I work from home it's important my devices are working too!

Thanks

Begona Dervish