Unable to create directory. Is its parent directory writable by the server?

Problem:
I tried to upload new theme in my new Wordpress blog, when I got this error:

Unable to create directory..... Is its parent directory writable by the server?

Solution:
The error is something to do with directory permissions,  so I logged in to my server through SSH, and changed the directories permission and it fixed the problem.

Other Possible Solutions:
If it happens that the directory permission is not the issue, please refer t this post for the proper solutions.