How can I overcome a 5 GB download limit set on internet by college server?
you'd need to know more about how this limit is imposed. For instance, do you need to log on to the college intranet with a username / password? If so, then it's tied to your account, so I'd say it's more or less impossible. If it's more simple than that - by IP or Mac address for instance - then force a refresh or move your computer to another network terminal, or change your Mac address using a tool such as "macchanger" for linux.
The key to understanding how to break these things is to know how it's done in the first place, so really need that before we can advise further.
Does this cap occur 24 hours a day? It might be worth checking if you have unmetered access overnight and if so scheduling your downloads and updates to take place during this period.