you can file a new w-4 for 2025 at any time. take into account that there are only 11 months left in the year so fewer pay periods
we can't see your tax forms or w-2 or know anything about your tax situation.
there may be things you can do to increase your refund like making a retirement a/c contribution or putting money into an HSA if you qualify or possibly other things. However, all these things will cost you more than the increase in your refund.
the $2500 was probably your withholding from your w-2.
$2497 was probably your tax liability resulting in the $3 refund.
