rraaddoo3 :
Currently I have Radeon R9 270 and I want to change it with Nvidia RTX 2070
My processor is i5-4440 3.10 GHz and I want to swap it for i7-7700k and Asus Republic Of Gamers STRIX Z270E GAMING.
Unless the motherboard and processor are in some bundle deal that makes the price significantly better, I would go with an 8000-series processor (and appropriate motherboard) instead, since Intel added more cores and higher clock rates at any given price point this generation. For example, a 6-core, 6-thread i5-8600K tends to perform slightly better than the 4-core, 8-thread i7-7700K, while costing a fair amount less. Keep in mind that either of these processors will also require DDR4 RAM though, and your existing system should be using DDR3, so you will need to buy new RAM. You'll also likely need a capable cooler if you are currently just using an Intel stock cooler, as these processors run hotter and don't include a bundled cooler, being unlocked "K" parts.
Another, more cost-effective option might be to pick up a used processor for your existing motherboard, since Intel's per-core performance gains haven't exactly been that large in recent years. For example, a pre-owned i7-4790K is only about 15% behind the performance of a 7700K, can be found for around $250 on ebay, and should work with your existing motherboard and RAM. Though again, you'll want at least something like a $30 tower cooler for it if you don't already have one. And if you don't have a Z-series motherboard, you won't be able to overclock, though a 4790K can typically only overclock around 10-15% anyway, and will require a fairly powerful cooler to do so.
As for the graphics card upgrade, such an upgrade might be a reasonable option, but an RTX 2070 might be overkill. Keep in mind that the 2070 will likely perform similar to a GTX 1080 in most existing games, and that it will likely be around $600 at launch, and probably won't be available for another month. Since the R9 270 is only about as powerful as a GTX 1050, another decent upgrade option could be a GTX 1070, which can currently be found new starting at around $370, or pre-owned for significantly less. At 1080p resolution, even a 1070 should run games quite well at max graphics settings, and would even be relatively decent at 1440p. It's also possible to find some GTX 1080s for under $450 new, quite a bit less than what the RTX 2070 should be when it launches. You would miss out on the fancy raytracing effects in the handful of games that are expected to support them in the near future, but as of now no games support them quite yet, so it's difficult to say how the feature will stack up in actual games.
Rather than choosing between a relatively expensive graphics card, or a relatively expensive CPU/Motherboard/RAM/Cooler upgrade, you would likely get better overall gaming performance by going with a more reserved combination of the two, particularly if you are gaming at 1080p, such as a used i7-4790K with a GTX 1070.