If you pay more than $7500 to the IRS through income tax deductions, you can ask to get that back when you file your tax returns. You don't need to change witholdings. Look at line 63 on your 1040 to see how much in fereral taxes you owe last year. That doesn't change regardless of how much tax you withold throughout the year. You will get up to $7500 back as a tax credit depending on how much you owed. If you owe less than $7500, you'll get all the money back. It's not a $7500 payment to you, it's reducing your tax liability by $7500.

You can simulate it yourself by copying your 1040 for 2016 and adding $7500 to line 54 (Form 8936) too see how that will change. It should drop line 63 by $7500, or zero, whatever is greater, which will also increase your refund (line 75).

Now, if you have less than $7500 in tax liability, there are a few things you can do to increase that.

1) Get more income from wages. 2) If you have stocks in a taxable brokerage account (not a IRA/401k account), you could sell some. Any capital gains are taxable income. 3) If you have money in a Traditional IRA, you could do a Roth IRA conversion. Any money converted to a Roth IRA is immediately taxable as income, but will continue to grow tax free. You may be able to roll over some of your 401k to a Roth IRA, which would be a taxable event (assuming it's a Traditional 401k, and not a Roth), however, you're generally only allowed to do this when you separated from your employer. You'd need to check the terms on your 401k plan to see what's allowed.