Welcome to the Dell Community  @Liminlime 

Sorry but you would need to replace the motherboard to upgrade the CPU.

https://www.parts-people.com/index.php?action=search&search=5578+motherboard

Your best options to increase performance would be an SSD and memory upgrade.

Dell Inspiron 15 (5578) compatible upgrades:

https://www.crucial.com/usa/en/compatible-upgrade-for/Dell/inspiron-15-%285578%29

Inspiron 15 5000 2-in-1 Service Manual:

https://www.dell.com/support/manuals/us/en/04/inspiron-15-5578-2-in-1-laptop/inspiron-15-5578-laptop-sm/before-working-inside-your-computer?guid=guid-5d3b1051-9384-409a-8d5b-9b53bd496de8&lang=en-us

Best regards,

U2

Welcome to the Dell Community @Tommy7777 

Here are a few things you can try to increase system performance!!!

1. In “System Properties” set  Performance to  “Adjust for Best Performance”
2. Then adjust “Virtual Memory” as needed.  “More is better but it uses Hard Drive space”
3. Reboot.
4. Do a “Disk Cleanup”
5. Then a “Disk Defragmentation” (Skip if SSD is installed)
6. Open an Administrative Command Prompt and Run chkdsk c:/f    “Yes to run after reboot”
7. Reboot.

Best regards,

U2

The Dell Inspiron 5000 is a lemon.  Anyone who owns one knows that after a year or so it becomes so slow that it is unusable.  Will not by a Dell again.

@Tommy7777​ Maybe it's just yours that was a lemon, mine's 7 years old and running as new.

i have dell inspiron 15 laptop and i want to update its processor for current version.

It is possible or not.