Thanks for the link. I used it with some small modification, because my problem was slightly different.
Originally Posted by milton1
I was running out of space on my root partition, so I needed to use a folder on my bigger partition as a download target for packages.
this removes the folder.
sudo rm -Rf /var/cache/apt/archives
sudo mkdir archives
. This last one is necessary because I had an error with that missing folder.
sudo mkdir ./archives/partial
4. and finally simlink to this folder from /var/cache/apt
sudo ln -s /path-to-folder-on-big-partition/archives /var/cache/apt/