You can use the stock management page to upload your stock values in bulk via a spreadsheet upload.
The spreadsheet you upload must be a CSV file. If you use an Apple computer it must be saved as a Windows Comma Seperated (.csv file).
Your spreadsheet should contain two columns labelled
Place the SKU code in the SKU column and the new stock quantity in the Quantity column.
Click the 'import stock' button (as indicated in the above screenshot).
A new window will then appear.
Select your import field using the 'choose file' button and then click import.
If your file is large please wait for the file to process. When its done you'll see a success message to indicate that the import is complete.