Mayby Website x5 did not close correctly. And it is still in memory, open up your taskmanager, remove all websitex5.exe in process tab. Then try again. Do this during update (directly after the update program has closed X5)

Opening taskmanager depend on you OS. cctrl and shift and escape is the most common keys (all together)

Or

Type in at start -> run -> taskmgr and enter