How can I remove negative comments from my project page?
You can not remove negative comments on your project page yourself. Part of the philosophy of betterplace.org is that interested people can create an individual picture of your project from all the information available to them. This includes critiques. You do however have the ability to respond to negative statements and present your counter argument in a comment.
However, should it be an irrelevant evaluation of your project, i.e. a personal attack, you can file a complaint at any time by sending an e-mail to firstname.lastname@example.org.