Here is the upgrade path (2 options) for upgrading from Brocade Network OS 4.x to 7.x:
4.1.3a to 5.0.2c FWDL with "coldboot"
5.0.2c to 6.0.2h FWDL with "coldboot"
6.0.2h to 7.0.2c FWDL with "coldboot"
4.1.3a -> 5.0.2c FWDL with "coldboot"
5.0.2c->7.0.2c FWDL with default-configuration
Note: Running config should be uploaded to FTP server for archive and restore purposes when needed, prior to the FWDL operation. For larger fabric, upgrade odd numbered RBs and then upgrade even numbered RBs, with the principal switch to be upgrade last.