what i would do:
1) update the mobo bios
2) swap the psu to the MSI MAG 650 (new):
https://www.overclockers.co.uk/msi-...0-plus-bronze-power-supply-pow-msi-03345.html - £48
3) swap the 3000g to a ryzen 5600 (used) - £80
4) add in another 8gb ram (used) assuming that the current ram is 3000/3200MHz - £25
5) add in a 9060XT 16gb:
https://www.overclockers.co.uk/xfx-...gddr6-pci-express-graphics-gra-xfx-05433.html - £330
6) add in a 1TB NVME SSD, assuming the board has a M.2 slot as you haven't specified which board exactly:
https://www.overclockers.co.uk/wd-b...pcie-4.0-solid-state-drive-sto-wdc-06213.html - £100
total damage = £583 give or take
other considerations:
a) CPU cooler for a £10-15
b) if the kid isn't a massive gamer (ie, simple games like fortnite only) then could potentially save a few bob and get a 9060XT 8GB instead:
https://www.overclockers.co.uk/asus...-pci-express-graphics-card-gra-asu-05199.html (£270)
c) the current case may need swapping out if it has not a lot of ventilation, you haven't said
realistically, there isn't much of a choice if you want to keep to budget
the cheapest new pc at ocuk is £800:
https://www.overclockers.co.uk/ocuk...-rtx-5060-pre-built-gaming-pc-fs-pb14-ep.html
this is also poorer in performance compared to the above
in all honesty, if you're unsure, just wash your hands off this request tbh.
you probably don't want to be their tech support in the future, either.