Raid 1 Hard Drive Upgrade

New poster here so I appreciate your patience. I think I have a simple question...

I have a PowerSpec B642 running XP Pro SP3 that has 2 - 250gb SATA hard drives in a Raid 1 setup from the factory.

What is the simplest (rookie here) way to do this. I have 2 brand new - 500gb SATA drives that I want to install. I've heard that if I simply replace 1 drive, the drive will mirror, then replace the other, same thing, but it won't recognize it as a 500gb drive, just the old 250gb.

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Can Acronis True Image make this simple (or another Acronis product).

Thanks in advance, this is my small business computer that functions as a server and I surely don't want to lose my files with things that "might work"...

Thanks...