The install CDs will only do a new install or repair (repair would wipe your current config but preserve VMFS partitions). With your case you would want to
1) Download the latest ESXi patch from here - http://download3.vmware.com/software/vi/ESXe350-200904401-O-SG.zip
2) Extract the ZIP and you'll find 3 ZIP file. Extract the one that ends with -I-BG-zip (it'll be about 44 MB in size).
3) Within that ZIP you'll find VMware-OEM-image.tar.gz - extract Dell.tgz from it.
4) Copy that over /bootbank/oem.tgz and reboot your host.
The install CDs will only do a new install or repair (repair would wipe your current config but preserve VMFS partitions). With your case you would want to
1) Download the latest ESXi patch from here - http://download3.vmware.com/software/vi/ESXe350-200904401-O-SG.zip
2) Extract the ZIP and you'll find 3 ZIP file. Extract the one that ends with -I-BG-zip (it'll be about 44 MB in size).
3) Within that ZIP you'll find VMware-OEM-image.tar.gz - extract Dell.tgz from it.
4) Copy that over /bootbank/oem.tgz and reboot your host.
Just to make sure: I should rename extracted Dell.tgz to oem.tgz and copy it to /bootbank correct?
Yes - the file dell.tgz has to be renamed to oem.tgz when you copy it to /bootbank.
One more thing: I should have installed latest patch on my ESXi server before I install/copy this Dell oem.tgz file?
Yes. If you were at update 4 for example and didn't want to upgrade, then you could download the update 4 zip file and extract the same file out.
Right now I have latest ESXi build updated using Windows update service.