what is the OS version of Vcenter ? If it is 32-bit then you need to create a new Server with 64-bit OS and use DataMigration tool to upgrade the VCenter to 4.1. If your VC is in 64-bit then it is a simple upgrade.
Kindly folow the steps provided in vshpere 4.1 upgrade guide....http://www.vmware.com/pdf/vsphere4/r41/vsp_41_upgrade_guide.pdf
Below links and Datamigration tool video also help you to upgrade the VC 4.1
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Message was edited by: tdewanjee