Do you want spend more money or less money?
Upgrade temporary?
Which GPU do you have?
As for me i5 still can be pretty powerfull for gaming. But if you are streaming that might be another pair of shoes.
Now for a part, you only game? You probably don't need more powerfull CPU than that, but if you wanna upgrade the only CPU to i7 it will hold 2 or 3 years.
But if you wanna upgrade now to i5 8400 you need new motherboard and new ram as it is different.
As @dontlistentome said "You could put an i7 47xx in your motherboard. Since you don't say what CPU you have, or what you plan to use the computer for, I can't offer more advice than that.
A move to a newer CPU means a new motherboard AND new DDR4 memory needs to be purchased as well."...