I have a free licence key (is it the reason ?)
Yes, that's the reason. Only customers with paid licenses can download it from VMware's web site.
However, if you need a specific version, you can build your own ISO/ZIP file using e.g. https://www.v-front.de/p/esxi-customizer-ps.html
Please be careful with updating your hosts in case they require additional (vendor specific) drivers.
Also be aware the 5.5 has been end of general support for almost a year at this point.
Thanks for your answer.
I Use a Dell poweredge 2900 it's enough for my development needs.
Do you think I can install a newest version of esxi in this machine ?
The compatibility matrix between the Esxi version and the Dell Power Edge 2900 Server is as follows:
I answer you only for this last question. I haven't checked the download link.
The latest version compatible with the Dell PowerEdge 2900 Server is the Esxi 5.5 U3 vmware version.
Sorry if I allow myself, but it is better to install a customized ESXI image officially released by DELL. I believe this is the last release of the 5.5U3-A12 released:
(even if your question is on the Esxi 5.5U3b version, my answer is just a suggestion)
I managed to download it without problems.
This is the official list... I'm looking for users that experienced ESXI version Switch
Sorry I didn't saw the second part of your message.
I'll try this file.
Ok! no problem.