You speak English very well,so I decided to help you:p
Well,yes,I recommend you use XS++...It is very fast and convenient...Anyway,DO NOT UPGRADE with SEUS...You won't be able to do anything...Firmwares,as you said,must have the same "number" let's say...
Search and learn...For the time being,I can only tell you that flashing your phone with a new firmware,is only the beginning...;););)