Upgrade Sugar 4.21b 4.51

[ATP]

Hello,

Could any body please let me know the steps involved in upgrading from version 4.21b to 4.51.
I tried to do it and am getting a fatal message. I would appreciate if somebody could outline the steps involved in detail.

Sugar enterprise suite version 4.21b
Here is my email
sswamy@atp.com

[sacramentojoe]

Whats the message? Are the directories writeable by the webserver user?