Thanks for the reply, may I ask why it’s not recommended to upgrade new guns ?
It's always risky tinkering with a sole gun, given the potential to make it worse, or unusable. The basic non-ETU G&Gs are solid candidates for clean-it-then-leave-it-alone reliable workhorses. They don't come with a big list of trick parts like a Specna or Lancer Tactical, but if you get a good one, they can work very well indeed.
I agree with
@Speedbird_666 that the stock motors aren't great, and that's an easy enough swap, as above (I like the value proposition of Big Dragon M140 motors bought direct from AliExpress, to chisel every penny, but there's more of a risk and a wait with them).
Electrics can be a bit trickier, but the Perun ETU++ does take the worry out of that. It's telling that Perun have come up with a mosfet specifically to sort the notorious issues with the G&G ETU.
If you want to fling more money at it, you can look at the parts in front of the gearbox. ZCI and AOLS barrels tend to be pretty decent for not a lot of money, but as always with Chinesium parts its entirely down to the example you receive. ZCI plastic rotary hop units work well, as do Maple Leaf hop rubbers and Maple Leaf (or clone) Omega nubs.
There's always a danger of introducing misfeeding or an air leak when fiddling with the hop and rubber, and they can be very frustrating to diagnose or fix as they only need a fraction of a mm misadjustment either way to manifest.
That risk can be ameliorated if you replace the barrel, hop unit and rubber as one, keeping the original G&G assembly aside and untouched. If you do have problems on game day, it's literally a couple of minutes to swap the original back in.
Just please be aware that "upgrading" an airsoft gun can make it worse, or no better than the original parts, which are all designed to work together. It's great fun to tinker, but generally after you have a spare to hand.