There are many ways to change the folder permission in your server. Here I'll show you two common ways:

1. Using your favorite ftp client such as Filezilla. (Download Filezilla)

a. Using your FTP account, login to FileZilla.

b. Right click on the folder and click "File Attributes".

c. On "Change File Attributes" window, check all options or type "777", then click "Ok".

2. Using the Cpanel file manager

a. Login to your Cpanel.

b. Click "File Manager".

c. Click on the folder that you want to change permission.

d. Click "Change Permission" link from the upper right corner.

e. Check all options or type "777", then click "Change".