gr346512 :
https://www.amazon.co.uk/ADMI-Intel-Gaming-PC-2400MHz/dp/B07BBNBNC8/ref=mp_s_a_1_10?ie=UTF8&qid=1543506300&sr=8-10&pi=AC_SX236_SY340_QL65&keywords=gaming+pc+i5&dpPl=1&dpID=41yfklXXNkL&ref=plSrch That’s the pc I have
Well... that doesn't help with the make/model of the motherboard. Take the side panel off the case and look at the motherboard around the center. The make/model should be printed on it. It may be partially hidden under the gfx card. You might need to know that before you buy the CPU to be sure your board supports it, and if you need a BIOS update for the CPU to be recognized.
You can also use
CPU-Z to ID the make/model of the board. It is usually correct.
Obviously it is an Intel board with an LGA 1151 socket. If I were you, I'd start with the new gfx card alone. See if that satisfies you. You can always add the i7-7700k later. But if the motherboard is not a Z class board, you won't be able to utilize the OC capabilities of the 7700K that you'd be paying extra for. In that case you might want to consider the 3.6/4.2GHz i7-7700 (non-K).
Of course, there's no reason you can't add both at the same time. I'm just trying to offer some cost-saving options.