You can increase your investment for deals that are still raising by navigating to the Deal Commitments page. Once there, you can click on the investment you’d like to increase. You’ll see language that says “You’ve invested [X] amount” with a purple “Increase Amount” link.
Once you've clicked on "Increase Amount," you'll be able to enter in your new commitment amount. Once you're ready, hit "Increase Amount" to finalize the change.