How to: Modify a Proxy (SQL Server Management Studio)
This topic describes how to modify a Microsoft SQL Server Agent proxy account. Only members of the sysadmin fixed server role can create, modify, or delete these proxy accounts.
After upgrading from SQL Server 2000 to SQL Server 2005, all user proxy accounts that existed before upgrading are changed to the temporary global proxy account UpgradedProxyAccount. The UpgradedProxyAccount is only granted access to those subsystems that were explicitly used, and does not have access to all subsystems after upgrading.
To modify a proxy account
In Object Explorer, expand a server.
Expand SQL Server Agent.
Expand Proxies, expand the subsystem node for the proxy, right-click the proxy you wish to modify, and click Properties.
On the General page, you can change the proxy account name, credential, or the subsystem it uses. On the Principals page, you can add or remove logins or roles to grant or remove access to the proxy account.