If you have 256mb on a computer and replace it with 2g because that is the total capacity will you lose your information?

Presumably you are talking about replacing (upgrading) system RAM, as its been a long time since 256mb or 2 gb hard drives were common.

That being said, replacing the RAM in your computer will have no effect on the data stored on your computer. Long-term storage of user data is done with the hard disk. System RAM is temporary storage only, and is wiped every time the computer is powered down.