You could try a manual upgrade which involved copying the zipped upgrade package into a folder and then calling a specific php path from your browser. There are instruction in the Install file that comes with the zip and several howtos if you search for them.

You should check that you do actually have zip installed and that you are not close to the files or filespace limits of your hosting account, as such a limitation could be preventing the unzip from running.

Finally, also check the file/directory permissions on the upgrades folder and that it is writable (0755 or 0777)

Thanks for answering.

How can I check if I have zip installed ?

Chances are it is available because you can already install concrete5 addons. A good way to check all that sort of thing is with my phpinfo addon (free) that gives you phpinfo from the dashboard. So install that addon and it will give you just about every bit of environment info you ever want to know and test 'installing' at the same time.