You will be allowed to increase your pledge level through the BackerKit survey. Depending on the Kickstarter campaign, some tier levels may be Kickstarter exclusive. 

Through your BackerKit survey, you will be able to switch your pledge tier through the survey itself by simply clicking the 'go to page' drop down on the top right side of your survey and select 'Welcome'.

From here you can select the 'switch your pledge level' that is located below the get started button.

For more information on this, check out the BackerKit Link below:
https://help.backerkit.com/article/596-how-to-switch-into-another-pledge-level