The switch has to be connected using the serial cable to a PC. After starting a terminal program (e.g. HyperTerm on Windows) logging in to the switch can be accomplished. The login data for a switch set to factory default is admin / password. To display already configured IP settings the following command can be used:  
ipaddrshow
   
fcsw11:admin> ipaddrshow
   
SWITCH
Ethernet IP Address: 172.18.0.299
Ethernet Subnetmask: 255.255.252.0
Gateway IP Address: 172.18.3.354
DHCP: Off
  Setting or modifying the IP settings of an EMC DS-300 is done with:  
ipaddrset

fcsw11:admin> ipaddrset
Ethernet IP Address []: 172.18.0.299
Ethernet Subnetmask []: 255.255.252.0
Gateway IP Address []: 172.18.3.354
DHCP [Off]:
  All modifications are in effect immediately. Because of the changed environment the switch restarts some of its services like the internal webserver. Clients, that are connected by SSH or web get disconnected. Reestablishing the connection is necessary for them.
Changing IP address settings does NOT interrupt FC traffic!