CPU upgrade

Specs say the Inspiron 3268 can use Intel Core i3, i5, or  i7 CPU. It has to be a 7th Gen CPU to be compatible with the Intel H110 chipset.

This site lists a Core i5 and Core i7 that are supposed to be compatible, but I can't confirm. And there may be other 7th Gen CPUs that are also compatible.

You will probably want to install the latest version of BIOS    before swapping CPUs, if you don't already have the latest version.

Read the Service Manual about removing the heat sink and fan. Then you'll have to carefully remove the old CPU from the socket and install the new one, without bending/breaking any of the pins on old or new CPU, apply a fresh, thin coat of decent thermal paste and reattach heat sink and fan to new CPU. Probably lots of youtubes about removing/replacing a CPU.

You may also have to clean install Windows to get PC to work with new CPU. So back up all personal files on external media, and make sure you have product keys for all your apps which will have to be installed. The Windows product key is embedded in the motherboard so you shouldn't need to enter it when you clean install Win 10.