SJS don't recommend using your Optymyse 4 hardware as it is old, no longer in warranty and not as powerful as hardware you can now purchase e.g. NUCs, Chromebox or Raspberry Pi.
However if you wish to know if the Optymyse 4 hardware you have is compatible with Optymyse 5 you simply need to check the USB ports on the back of your receivers. If the USB ports are blue you have V2 boxes which means they should be usable with Optymyse 5 if they are black they are not compatible with Optymyse 5.
Not compatible (Optymyse receiver with black USB ports)
Compatible (Optymyse receiver with blue USB ports)
Please note: Due to the age of the devices and the scarceness of replacement parts SJS can only offer best endeavours support and are not responsible for the performance of the Optymyse 4 receiver boxes with Optymyse 5.