Update:
I found "/var/log/journal" took up 143.1M space! After deleting the directory, I got enough space to transfer sketch. Here is the space available now:
Filesystem Size Used Available Use% Mounted on
/dev/root 463.9M 310.6M 117.5M 73% /
I only experiment with Edison for a couple of days. How can the journal log eat up so much space. Is this a bug?