Installing theme taking forever/frozen

I have just bought a theme from themeforest (Reason) and spent all evening trying to upload it. I get as far as the page that says:

‘Installing Theme from uploaded file: themeforest-2274642-reason-wp-smart-responsive-customizable.zip

Unpacking the package…’

but however long I wait, it never gets any further. I have tried refreshing the page and restarting the upload from scratch.

How long should it take??

Please help!