Sorry, your server came pre-installed with the trial version (which is not a "demo") of the ESXi version 7.0U3 customized by DELL, but you want to update it with the standard version (let's say the "generic" non OEM specific version). In my opinion, you would do it sooner and save yourself possible problems by using the corresponding DELL customized image for ESXi product version 8 which you can download via the "VMware customer connect" (usually the recommended approach, unless there are specific reasons).
Thanks for your comment,
iDRAC is probably not configured (I need to give a look on it). My problem seems to be linked with DellEMC Customized version of VMware ESXi Image. I need to found a new image for 8.0 version. I asked to the Dell support but no answer.
Thank you for your explanation. You are totally right. But it seems there is no custom DELL ESXi 8.0 image yet.
I'll wait for Dell's response.
Actually, I'm using a 7.0 trial version (completed in a few days) and I have a real 8.0 license that I can't use.