This site gives some good examples of how it can be done through the terminal. Although it most cases it's probably not needed and or you won't notice much difference in 'speed' of downloads..

https://linuxconfig.org/how-to-select-the-fastest-apt-mirror-on-ubuntu-linux

The tool usually used in Ubuntu to do this through a gui is not included in LXLE as it requires the update notification daemon running in the background at all times which sucks up a ridiculous amount of memory for such a mundane task.

Which is why I came up with a relatively unique way to notify the user with update notifications. LXLE is setup to automatically install security updates by default. To do that it occasionaly queries the repositories for updates to see if there are any security updates to apply, any thing else that is found is not updated but on start up of LXLE that list is queried and if any other updates are available it tells the user they are available. All this is done without any need for memory to be constantly wasted on something running in the background full time. :) Pretty slick huh... lol