Old computer is slow install windows 10 or insert RAM First

So it has been a task to update every computer that has window 7 to window 10.

During the time of gathering data, someone call’s me to help because his computer works very slow, and chrome doesn’t work at all.

so I went to meet him and I started removing the temporary files and unusual files that are located in it, and I did some poking since the user left for a meeting.

I noticed that his CPU was running at 2.40 GHz and it has 4GB of RAM.

whenever I go to task manager and whenever I load the chrome or change the settings or websites on chrome the CPU runs at 100%.
So the question is.?
If I bruised I should put more RAM into the computer or install window 10 first to make the computer more reasonable to use.

So my brothers please share your thoughts on it
Thanks a lot.