I've been trying to get windows 10 updates onto my parents pc, its been failing every time when they're directly windows related. The microsoft office updates go through no problem (for security and whatnot).

I have a feeling that the hard drive is failing, but once it gets past trying to update it runs correctly...it just takes a decade to turn on.

Anyone have any experience like this?

Also if i want to replace the 1 TB harddrive with a 500gb SSD what is the process for salvaging files from the existing harddrive and installing the new one?

Can download update packages 1 by 1 manually and install. When you say it fails does it give you an error code?
You would need to remove enough data so you can repartition the drive to the same size as the new one partitioned.
something like 470gb or some shit idk not doing match right now. then use clonezilla to do a bit by bit copy of it to the ssd.
will need to plug in both drives to do it so either an adapter for external connection or another pc to connect both devices.

Ill check the error codes when im back tonight. I might just do a fresh install of windows on the new drive, does that change the proper way to go about it at all?
Could i reinstall windows on the new one then just use the existing harddrive as a large storage and transfer over the files i need afterwards then?

Fresh installing would be best regardless for many minor reasons aside from the main one which is saving time.
You would need an adapter or hard drive enclosure though to connect it unless the laptop supports 2 internal drives.

Its a desktop FWIW

Sry its still early idk why I was under the impression it was a laptop.
either way you know whats what now.

You could download 1703 to an flash drive and run the Command loading it directly rather then using updater. Fresh install would be best bet to avoid any further issues though