I have found that a laptop that is painful to use with Window10 can be useful running a light version of Linux of some sort. It will do office stuff with ease with 4Gb. And Libra Office comes with just about any Linux Distro. Image editing may be another matter.

The greatest improvement will be replacing the spinner with an SSD. Even a little one like 125Gb will make an older system will seem like it’s given a new life when an SSD is on board.
As long as you don’t go nuts with lots of media, 125Gb will run Win10 just fine. And they are nearly free with a happy meal these days.

A system that is way slow with a spinner is just like a breathe of fresh air with an SSD.

Given a choice I’d go for the SSD first. Especially if Win10 is going to be the OS. Do a power on start then open up the task manager and go to the performance tab. Watch how much time the mechanical drive stays at 100%. Win 10 really sucks on the drive a lot.

Go to the Crucial Memory web site and you can look up what kind and how much memory your system can use. Some older systems can only handle 4 or 8Gb max.
For most apps you don’t need more than 8Gb.

Dell desktops have a very annoying hard drive mounting system. The friggin power cables expect the drive to be in a very precise location. I’ve made adapters for 2.5 SSD to 3.5” trays out of cardboard. The trick is to position the connectors in the right place.
Usually you need a right angle connector at the drive because the drive bay puts it right up against the case door.

All the Best,
Jeff