How to customize the Logo of Production portal using Community Edition?

Iam trying to change the logo of production portal following the below steps.
1. Backup the Bonitasoft database
2. Extract the two files Content.Zip and CSSContent.txt from the Bonitasoft database table Theme (these are BLOB columns (CONTENT and CSSCONTENT respectively))
3.Make changes according to this post (when I find the link I'll let you know)
4.reZip Content.Zip correctly
5.Import the two files Content.Zip and CSSContent.txt to the Bonitasoft database table Theme overwriting the previous data (CONTENT and CSSCONTENT columns respectively).
Iam able to find the BLOB columns(content and CSScontent) in the table Theme,but the problem is these columns are showing up NULL.
Kindly guide me on how to customize portal on database backup?

Regards
Meghana