How can I increase the capacity of my /home/rob/downloads folder?

My downloader, yes it is sabnzbd, says I have too little space in my home/rob/downloads folder, no idea on how to increase a folder size though...... Please some help is much appreciated! Yes, I am a newby

1. buy a new disk or find an old one that is suitable
2. partition, format (mkfs) in any way you like
3. mount it e.g. at /mnt/temporary/ (mkdir first)
4. mv files from ~/downloads onto it.
5. re-mount the same partition at /home/rob/downloads
6. create a fstab entry to have it appear mounted at boot

hint:
$ mount -t auto /dev/sdc1 /home/rob/downloads

Google "move /home" to get direct help, it will not be exactly what to do, but it will contain a lot of very similar things.

You will be learning a good bunch of new stuff.
And finally think! - that is all you need.