Setup Error

Can anyone help me with solution to this error. I am installing gibbon on a domain and have encountered this below

The directory containing the Gibbon files is not currently writable, or config.php already exists in the root folder and is not empty or is not writable, so the installer cannot proceed.

Need help urgently please.

This is a duplicate post from this:
https://ask.gibbonedu.org/discussion/2543/setup-error#latest