Yes, we will have a pledge manager after the end of the campaign. In it you will be able to adjust your pledge as you see fit. You can pledge for any amount now and then upgrade to any pledge level later.
Keep in mind that adding funds during the Kickstarter campaign, helps us unlock more Stretch Goals, which is something that benefits all backers! So, if you can at least pledge at the minimum reward level, then that would help the project grow.