I have a Dell inspiron 15 5567 with the i5 processor. But i would like to know if i could upgrade to an i7 and how

Laptops as a 'rule of thumb' are not 'upgradeable' that way for 'off the shelf' systems, unless you buy into a special model series that has 'some' upgradable parts. CPU is NOT one of them, because they are actually SOLDERED to the Motherboard.

Secondly ANY change to the CPU or Motherboard immediately makes your Dell (OEM) copy of Windows FAIL, because it is coded ONLY for that hardware configuration you bought. You would also have to buy a brand new copy of Windows and then wipe and reinstall everything from scratch.

Lastly, unless you spend $1200 or more on a laptop, NONE of the laptops generally sold are 'gaming' laptops, so even swapping the CPU for a i7 wouldn't make your 'gaming' better if that was your intent. You want to mobile game, you have to pay HEAVY for that privilege, there is no 'shortcut'

Some Dell laptops can have their CPU and GPU upgraded with no need to change the motherboard. I had a Dell Precision M4600, and upgraded both CPU (i7 2720QM to i7 2860QM) and GPU (Quadro 1000M to Quadro 2000M). And its OEM Windows 7 Professional wouldn't fail. I didn't even have to reinstall it.

You completely missed I said "Laptops as a 'rule of thumb' are not 'upgradeable' that way for 'off the shelf' systems, unless you buy into a special model series".

A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination.

The logic behind your statement INFERS ALL laptops should be upgradeable BECAUSE you bought ONE maker's ONE model that does. Your countering the OP / ANYONE could walk into Walmart and grab ANY maker / ANY model laptop and it would be upgradable just because you had ONE specific Maker and MODEL that did.

I don't have the time to list EVERY MODEL just from Dell, then include EVERY MODEL from Sony, Lenovo, HP, Samsung, Acer, etc. for the past SEVERAL YEARS since your 2720QM and hand COUNT a exact number of 'upgradeable' model VS non upgradeable models. If you took the time to do that or had 30 years of EXPERIENCE I have that the difference (aka RULE OF THUMB) between UPGRADEABLE laptops VS NONUPGRADEABLE laptops would show your statement has no weight at all.

Don't argue a opposite point just to argue a point there IS a exception.
One or a handful of exceptions does not make it a RULE.