Backup to larger hard drive - memory size not recognized

I replaced my hard drive with a larger hard drive. The old hard drive was newly infected with a virus. I used the Acronis backup program and I am back up and running. The concern is that the system still shows the memory size of the old drive.
How do I get the computer to recognize the size of the new hard drive.
Dell Dimension 8400. Old drive 145G new drive 350G. Windows XP. Backup was performed from an external hard drive(my book). Thanks.