BIC lighters are designed with a fixed flame size and there's no mechanism to change it. If the flame seems too small or too large, it's likely due to the lighter needing a refill or a cleaning.
Here's what you can do:
* Refill the lighter: If the lighter is out of butane, it won't produce a strong flame. Simply refill it with butane.
* Clean the lighter: Dust and debris can clog the lighter's nozzle and reduce the flame size. Use a small, dry brush or a toothpick to clean out the nozzle.
* Check the flint: If the flint is worn down, it won't spark properly and the flame will be weak. Replace the flint if necessary.
Important Note: Never try to modify or disassemble a BIC lighter. It's dangerous and can void the warranty.