If you have the key, which on that vintage of machine was still on the sticker typically on the bottom of the laptop, you can download Win 7 from MS. I know with Win 10, they give you a choice of downloading and ISO to burn to a DVD or it'll create USB media for you. Link is here:
https://www.microsoft.com/en-us/soft...nload/windows7
Just make sure you've got your ducks in a row first. Make sure you'll have access to the source installation media for your applications, or able to re-download them to re-install. I also typically grab the drivers from the OEM site and put them on a USB stick for easy reinstallation after you load the OS just in case it doesn't find them. NIC/Wifi drivers there are really the most important since, if you can get reconnected after the reinstall, you can grab anything else you might need.
I happen to like Win 10 but I understand some folks don't. I did this a couple of years ago with a decent HP all-in-one. I got it with a regular hard drive and Win 7. I wanted SSD with Win 10. I swapped them out and installed Win 10 from scratch on the SSD. Problem is... Win 10 wouldn't activate as the PC had never been upgraded to Win 10. It was still during the "free" upgrade period so... I put the regular drive back in, "Upgraded" to Win 10 which generates the "key". I then swapped the SSD back in and was able to install from scratch, and activate. I just didn't want the "upgrade" install. I wanted "clean".