Upgrade plumbing 1/2" to 3/4" pipe?

You can but after that's all done you will just be out the extra money with no difference. You are failing to realize the incoming pressure will remain the same and will not increase flow.

Not worth the trouble. The 1/2 inch pipe will handle a ton of pressure so call your water company first to see if they can cut it up at the street. Also if your fixtures are the older ones that do not limit the amount of water, you can buy the newer ones. They still have good pressure and use less water. If I paid a water bill, I would rather have a toilet that uses 3 gallons of water versus 8 gallons.

This sounds like what i had. My old 1/2 pipes were so full of corrosion that i got very little flow and when the toilet was flushed i got almost nothing at kitchen sink. So i took out all the pipes from meter and replaced with 3/4 plastic. Now plenty of water and pressure

It will depend somehow on the diameter of the pipe. For example, if we have a 2 meter diameter pipe, it will just fit through the 2 meter passage. If it's more than 3 meters long, it won't go around the corner. If it's 3 meters long, it will just fit the 3 meter passage when carried sideways. In other words, in our 2D visualization of the problem, the pipe needs to be modelled as a rectangle, not a line segment.

You can do what ever you want and yes..... expanding the circumferene will reduse the flow but you can put an in line booster punp!