Unlike modern versions of ESXi that feature built-in HTML5 browser consoles, ESXi 5.5 relies heavily on the legacy standalone Windows application known as the vSphere Client (or C# client).

If you're currently using ESXi 5.5, it's recommended that you upgrade to a newer version, such as ESXi 6.7 or 7.0. Upgrading to a newer version provides several benefits, including:

Because ESXi 5.5 is legacy software, hardware vendors often still host their custom ISOs: Dell Support