Synthetic oil should be changed around 5,000 to 10,000 miles.
Conventional oil should be changed every 3,000 to 5,000 miles or at least once per year depending on how often you drive.
Some people drive only 5,000 miles per year while other people drive 12,000 miles per year and if you do drive 12,000 miles per year then you would likely need to change your synthetic engine oil every 6 months which is twice per year.
I change my synthetic oil every 8,000 miles although it's supposed to last for at least 10,000 miles and sometimes longer.
A new engine or new car costs much more than an oil change so I change my oil as often as I can to protect my engine and extend the engine life.