The others are correct about snail mail.
But if you want to use the internet this is how you can do it.
- Pack and split into 700Mb files (tar, zip or rar will do)
- md5sum all the files (so you know that they are the same on the other end)
- scp or rsync with ssh (rsync will help you if you need to resend)
But beware, it is going to take some time.
Let's say your uplink is 20kB/s.
The data is 20GB => 20 000 000kB.
Then it would take approximately 20 000 000kB / 20 kB/s = 1 000 000 s = 277h = 11 days...
And if we say that snail mail usually takes 3 days.
That means that you need to have a connection with a uplink speed of about 70-80kB/s if you are going to be faster...