This FAQ was written for QuickBooks 2009, older editions may have some variations, but is basically the same process.
IMPORTANT- You must be logged into QuickBooks as Admin to complete a company file restoration.
1) Select FILE from the QuickBooks toolbar.
2) From the drop-down list select Open or RESTORE Company...
A QuickBooks Open or Restore Company Backup dialog window will open
3) Click the Restore a backup copy radio button, click the Next button
4) Click the Local Backup radio button, click the Next button
5) An Open a Company dialog window will display, in the Look In field select the directory or folder where your QB company file backup copy is kept, double click the backup file name
6) A Where do you want to restore the file? display will inform you about overwriting the existing company file, click the Next button
7) A Save Company File as dialog window will open, in the Save In field select the directory or folder where you want to restore the backup file (if a company file already exists (and it should) you will receive a warning asking if you want to replace an already existing file) click the Yes button
8) A Delete Entire File dialog window will display a caution warning asking you to type 'YES' to confirm permanently deleting the existing data file, type YES and click the OK button
9) The QuickBooks Home page will be displayed with your current company file information
You QuickBooks company file has been restored.