I believe Toxic's guide shows to use the pen tool, which is the best way to do it.
However, if you are having difficulties, you can try the Magnetic Lasso Tool, play with the settings(feather, frequency, etc).
It should be a somewhat simple image to cut out, what problem are you having exactly, that way we can help better answer your question?
“Anna, my strong, terrifying Anna.” -Cas
"You lack the requisite spine and testicular fortitude to study under me" -Elodin