In VERSIONS_FILE [versions.txt], I have changed the version to 'roundcubemail:0.5:935ba49c33fe4815961e0709c3f7d0cf' from the old one and applied the specified steps.
[root@server56 custombuild]# ./build set autover no
Changed autover option from yes to no
[root@server56 custombuild]# ./build roundcube d
cp: `/var/www/html/roundcube/logs' and `/var/www/html/roundcubemail-0.5.1/logs' are the same file
cp: `/var/www/html/roundcube/temp' and `/var/www/html/roundcubemail-0.5.1/temp' are the same file
Editing roundcube configuration...
Roundcube 0.5.1 has been installed successfully.
WARNING: Database schema needs to be updated!
Open /var/www/html/roundcubemail-0.5.1/SQL/mysql.update.sql and execute all queries that are superscribed with the currently installed version number