Searching and replacing text in your database is easy using the SQL command:

     UPDATE table SET field = REPLACE (field,'pattern','whatever');

I've always used this command to remove styles and colors inserted into the contents by the WYSIWYG editors by my clients. You can execute this command through phpMyAdmin from your hosting panel or if you're stuck without it you can always use one of the database management tool for Joomla! Art Adminer is great and it will let you access other databases on the same server too!