Well you don't "have to" - how much money do you want to spend, in Euros?  Are you completely prepared to reinstall all your software including operating system?

If you decide you want to do a processor upgrade, you're really talking about at least 4 items:
Processor itself
A new motherboard that supports the new processor (your current one DEFINITELY will not support any Intel processor)
New video card that supports the new motherboard - although perhaps you can look at a motherboard that has an integrated video card, I can't recommend that
New memory that supports the motherboard - there's a risk that your current memory will not work with the new motherboard, and very likely your current memory will not combine well with new memory

You probably are going to need a new power supply as well, because the power consumption of the new processor and video gear will probably be too much for your current power supply.

And ... you may need a new case too, because the new power supply .... may not fit in your current case.  As you can see this rapidly goes crazy and you are selling your cat and maybe some organs ...

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