You didn't provide enough details in your question that could be answered specifically. What model scanner are you using? What are you trying to scan?
Generally, you cannot alter the physics or the optics of the reader. There may be a setting that could provide different ways to improve read reliability, but they would be very model specific.
Are you trying to scan a printed barcode, or a cell phone barcode? Some scanners have settings that change the illumination source making reading of cell phones more reliable.
My recommendation would be to ask your scanner vendor for their advice. They may have a firmware upgrade that improves read reliability for your model. Or perhaps you will need to purchase new scanners to achieve your speed goals.