install bigger drive on mac mini

It depends on the model year of the Mac mini. 2014 and earlier models can be upgraded but 2018 and later cannot as the drives are soldered directly on the board.

OWC is a well-respected source for either SSDs or HDDs and have install videos. See: https://eshop.macsales.com/installvideos

and https://eshop.macsales.com/shop/ssd/owc/mac-mini

How old of a mini are you talking about? Any old enough to use a hard drive can be upgraded. Newer minis with SSDs cannot. They're soldered onto the logic board.

You can also simply add external drives to your Mac to increase your storage needs. Photos, music, and especially video content can take up huge amounts of storage that can easily be moved to external drives freeing up tones of space. Pretty much everything you see in your home folder can be moved.

I keep all my photos, music and movies on an external drive and it works quite well along with all my documents. my reason is that I can easily share it between different macOS versions I am running but I also do it because I prefer having my internal/system drive to be just OS and apps.