The higher the allowances you claim on Form W4, the less tax they withhold. When you withhold less tax, you have less to be refunded when you file your return.
Most people would not receive large refunds by using 2 allowances.
Allowances have zero impact on the taxes you pay. It only impacts you much you have taken out of your pay.
If you want a larger refund, you'll need to lower the allowances to 0 or 1. But, then you'll have less take home pay.