Using Sharepoint Designer outside of internal work network

So I'm trying to use Sharepoint Designer to finish up some work over the week end, but it asks me for my email (which I enter) then it tells me it can't access it because of sharepoint foundation, etc. 

It works only if I have my PC connected to the internal network at my workplace. But a co-worker told me it's possible to use Sharepoint Designer outside of the network. 

Is this true? If so how? 

Thanks in advanced.

P.S I have permissions to access remotely by the way.