i'm not a sifu,
but we need to upgrade our leg first.
then upgrade the gears, slowly.

When I started with my first foldie, an Eco C7, I found an 8 speed rear cogs and wanted to upgrade to 8 speed. Together with an appropriate shifter, I went to a bike shop in Bdr Mahkota Cheras to get it changed. Although I know how to do it, I didn't have the tools at that time so I rather pay to get it done. First thing that 'sei ngan chai" says when I told him, he said, it can't be done as the frame can't take more than 7 speed.  So, I just ask him to take off the rim and change the cogs only. After much hassle he did it but the hubs were long on one side and shorter on the other. He can't take out the cogs again!    I have to buy my own set of tools and later the Eco C7 was modded to 27 speed! modded by myself. Most bike shops can't be trusted or rather they only want to untung the easy way. Anything that's not worthy, they become choosy but most don't have the skills actually.

i agree, plus they didn't even know how to tune the bike properly.

You and me, same case. Not including the experience of spray painting bikes when I was schooling (dismantling and assembling back again) I was also a mountain biker in the Y2Ks era. That was disc brake just started emerging and those days they use the lethal DOT brake fluid which leaked onto the paintwork becomes like a paint remover! Even from those MTB days, I buy just frames and assembled components that I liked. Those days components like Shimano XTs and XTRs, Mavic rims, DT Swiss made spokes only and now they makes rims too. Maguras etc etc were affordable. These stuffs are so expensive nowadays. Even brands like Kore and Ritchey were considered 'capalang'    Seems they have grown into the good brands category.

Now I tinker in folding bikes, I can't get frames alone. And now I have loads of 7 and 8 speed cogs, shifters, original V-brakes etc. Except for the bottom bracket nothing much has changed about the bikes. Those days there's only square taper now we have Octal Link, ISIS, hollowtech, press fit which all uses different tools. Part from that, the bike is still the same.