You buy a APU for the excellent integrated graphics.
But, there are no real good upgrades, particularly for a gamer.
If you install a superior discrete graphics card, you will have thrown away the big advantage of the APU.
Then, you are left with a relatively weak cpu. Most games depend on only a few fast cores.
Bottom line.....
What you get with a APU is what you will live with forever.
Yes, a A10-7850K will be an upgrade.
Your A4-4000 has a passmark rating of 1805 and a single thread rating of 1112.
The single thread rating is most important for cpu dependent games like CSGO.
The A10-7850K has a rating of 5493 and a single thread rating of 1572.
That is as good as you can get with your motherboard.
But, I wonder if spending $150 or so for such an upgrade is worth it.
By comparison, a G4600 at half the price has a rating of 5142 and a single thread rating of 2042.
You will need a lga1151 motherboard for $50 and 8gb of ddr4 ram for $70.
The lga1151 motherboard can support future processor upgrades all the way to i7-7700K