If your laptop came with DOS, then you can get a key from
@Ra.hul here on the forums. Optionally look at ebay. This is the easiest way out.
If you want to go the KMS route as mentioned by
@kuduku - you need to install a copy of Windows 8.1 Pro, activate it using a KMS key, upgrade to Windows 10 1511, check activated, and follow up with upgrades to 1809, and finally 20H1/H2. I would not recommend this method as your machine seems ancient. It might be better to do this if you upgrade to an SSD plus at least 8GB of RAM - which is required by Windows 10 for smooth operation. Plus this is fairly technical as well.
For those trying the KMS method, I only prefer this because I am pretty sure most of the keys being sold are not genuine or licensed correctly and could be blacklisted at anytime. And the money does not always go to MS, sometimes, its stolen keys etc which makes me squeamish.