I nearly used the mirrorsources.list by default but didn't want users to run into an unforeseen problem. However I did leave the altered list in the /etc/apt directory on purpose so whomever would want to use it could. Simply rename your current sources.list to something like sourcesoriginal.list and then rename mirrorsources.list to sources.list
Do a sudo apt-get update in the terminal or launch synaptic or the update app and watch the sources automatically determine your closest mirrors to download software from.