^^^ If you need instructions for Paint, see here:
https://win10faq.com/how-to-resize-photos-in-windows-10/
However you really ought to have a
decent image viewer on your computer (which definitely excludes the pathetic offerings that Microsoft provides with Windows). Irfanview is by far the best freebie:
https://www.irfanview.com/
As well as being an excellent viewing program, it's got loads of great editing facilities hidden away 'under the bonnet'. For example, when viewing an image in Irfanview you can simply go to Image > Resize/Resample to be offered lots of ways of resizing the picture. (Once you've done so, go to File > Save As to save the resized image to your chosen location).