Help replacing front derailleur Evening, total newb question maybe but it’s driving me mad. 

I have a Carrera Vulcan 2015 model which I bought second hand to aid my physiotherapy. From what I can work out by the spec sheet the front derailleuris a Shimano Tourney FD-M190 (I think, I say that as spec sheet says 27.5 inch wheel which is ). 

What could I replace this with? I haven’t got a clue and the lad in the bike shop literally said “dunno” and shrugged his shoulders. 

Rear derailleur is a SRAM x4 with a 8 speed Shimano cassette (which could do with replacing (I assume all 8 speed cassettes are the same). 

Thank you for listening and any help would be hugely appreciated. 

Paul
As far as I can tell the 2015 Carrera Vulcan came with SRAM X4 all round. If the front derailleur is a Shimano unit it definitely was not original. I would guess the previous owner swapped it in. A Shimano unit will have 'Shimano' and 'Tourney' written on it. A picture of the derailleur added to you question will help us provide a good answer. 

In general SRAM and Shinano derailleurs and shifters are not compatible because they use a different cable pull ratio (how much cable is pulled to move the derailleur a certain amount). 

You options for replacement depend on what front shifter you have. If the shifter was also replaced with a Shimano unit you'll need a Shimano derailleur replacement. I'd avoid the Tourney range and upgrade slightly to something in Altus or Acera ranges. The exact model you want depends on if the the cable routing comes from the top or bottom of the frame. 

If the shifter is still a SRAM unit you the obvious choice for a replacement is a SRAM X4 unit as was originally fitted. I don't think SRAM makes these anymore but they are available from Ebay, Amazon etc.