To configure Debian systems to update from mirrors.iu13.net, you need to add mirrors.iu13.net to your apt sources list.
This mirror provides binaries for amd64, i386, arm64, and armhf architectures.
The script provided below automatically backs up your current apt sources list and adds entries for mirrors.iu13.net. It does not remove your current sources.
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak ; echo "$(cat /etc/apt/sources.list.bak | sed -n 's/http.*deb.debian.org/https\:\/\/mirrors.iu13.net/p' | cat - /etc/apt/sources.list.bak)" | awk '!seen[$0]++' | sudo tee /etc/apt/sources.list ; sudo apt update
If you need to undo the changes, execute this command:
sudo cp /etc/apt/sources.list.bak /etc/apt/sources.list
If you just want to download the latest Debian ISO, see debian-cd instead.