Upgrade Server 2003 Standard R2 to Server 2008

I need to upgrade to Server 2008 Std from Server 2003 Std.
How do I get to do it or where can I get notes on the upgrade?
The Server is an HP Proliant ML350 Quad Core with a 2.5GHz Intel Xeon Processor; 1GB RAM, 4 x 300GB SCSI HDD 15k rpm, 20User Lics.