I have a 1/2" water line into my house from the meter. I would like to change that over to use a 3/4" or a 1" line into my house. Do I need to replace all the 1/2" pipe back to the meter with my larger line, or can I just start replacing it inside the house? I'm concerned I will lose pressure if I don't replace it back to the meter.
I'll disagree a little - LESS 1/2" pipe has less restriction than MORE 1/2" pipe. Now, in most cases the pipe outside your house is far more than the pipe inside your house but depending where the meter is, if it's a short run from where you increase it to the meter (one of those deals where it's sitting on the outside wall of the house, say, and is fed by a larger line) and it was formerly the case that the entire water service in the house was a single 1/2" pipe, you might well see a noticeable improvement (though it is of course better to have a larger pipe all the way back to the meter.)
Now, if there's 100 feet of 1/2" pipe from the house to the meter, or from the water main to the meter, you're not going to see much improvement if you change 20-30 feet inside the house. But if it's 3 feet to the meter and 30 feet inside the house, you will notice an improvement.
And, if you want to get sneaky, you can have a huge improvement (for a set number of gallons) by installing a pressure tank (as for a well pump) in the house (along with larger pipe, or a PEX manifold and a lot of home runs), so the 1/2" line is not required to supply water as fast as you use it, until you draw down the pressure tank. Not much help in filling the tub, lots of help in refilling the toilet when it flushes without dropping pressure to the shower precipitously. How many gallons would depend on how big of a pressure tank you buy, and how much your pressure varies with use (now.) Just to toss one out there, especially for the folks with a charge by size of line into house. More extreme setups might throw in a booster pump, too; I'm not going to suggest that without more data suggesting it would be worthwhile...
If you want more water pressure you have to go all the way back to the meter. Doing this usually involves local water company. Mine doesn't care if you do the work but they have inspection steps.
You could start replacing things in your house but this won't help your water pressure situation - until the main line gets replaced.
As Ecnerwal says, if you can reduce the amount of 1/2" pipe, you'll increase your pressure. That said, most homes have 1/2" pipe to and from most of the fixtures. You don't need to and will find it a hassle to run supply to sinks and toilets in 3/4".
You might look and see if you have a large brass pressure regulator near the entrance of the water main to your house. This device is designed to down regulate excessive street pressure. However, in your case, it could either be out of adjustment (usually has an adjustment bolt on top) or malfunctioning. These devices typically approach $100 new so they aren't inexpensive to replace but they do typically have unions attaching them to the main pipe so you may be able to replace this yourself if you have some plumbing skills.
Another possibility: do you have older galvanized pipe or another pipe type that could have corrosion in it? This isn't typically a problem with copper.
Do you have 1/2" pipe installed thoughout your house? If you do, increasing the size of your pipe outside of your house to 3/4" will not help. The 1/2" piping inside your house restricts your flow. If your piping from the water meter to your house is 1/2" and the house piping inside your house is 3/4" or above then replacing the piping outside your house will increase you're water flow. This assumses your water pressure at your meter is steady.