You're looking for a link to the BIOS update for the Acer Aspire 5749. Here are some steps and resources to help you find and download the correct BIOS version:
This guide provides the direct steps to find the official download link and instructions on how to safely perform the update. acer aspire 5749 bios link
Step 5: Automatic reboot. After the flash completes, the laptop will reboot. On the first reboot, you may see a message: “New BIOS detected. Press F2 to configure.” Press F2, then Load Setup Defaults, then Save and Exit. You're looking for a link to the BIOS
How to update the BIOS: