Sometimes you might want to give further support to a project by upgrading your pledge level to another. Please see this help article for details on how to upgrade your level of support.
If you do upgrade it's worth bearing in mind that by upgrading you move from one pledge reward level to another. Upgrading does not mean that you get the reward items in the new level in addition to the rewards from your previous level. So please do make sure you choose carefully when pledging or upgrading or you might lose out on the reward that you really wanted.