1) Do i only have to insert a license key?
A : yes
2) do i have to install something or insertin the license key is enough ?
A : you do not need to install a license server for ESXi 4.1. It only for older versions
3) do i need to be the owner of the free license key or the new license will just substitute the old one?
A : Not required to be the owner, you Just need to insert the key on the Host and vCenter server
4) will all features be unlocked?
A : Not all the features , Just the features that are available for the Essentials licenses
VMware KB: vSphere 4.1 Licensing and Sales FAQ
5) is it true that i need to reinstall esx in order to have service console?
A : I do not understand this question .? what does licence has to do with service console..? ESXi 4.1 does not have a service console in the first place only an ESX 4.1 classic has a
service console
Thanks,
Avinash