Access the keyboard with:

Keyboard.current

Pressed this frame:

if (Keyboard.current.spaceKey.wasPressedThisFrame)
{
    Jump();
}

Held:

if (Keyboard.current.wKey.isPressed)
{
}

Released:

if (Keyboard.current.spaceKey.wasReleasedThisFrame)
{
}

Always consider checking whether Keyboard.current is available before using it.