When you install Ubuntu on a computer, you'd normally go through the installation ISO which guides you through a wizard where you select your location among other things, and that means you get connected to the mirror closest to your location allowing timely updates.
But for those of us who flash Ubuntu images on Arm SBC's, the mirror is normally fixed to the one set by the developer be it in China or Slovakia, or defaults to the US mirror. It still works, but it can be slower than necessary.
In a computer, an easy way to change that