How to edit and delete our comments/topics on these new forum?

A real mess, I prefer the old forums.

You have to reach member level to edit posts after the 4 hour time limit and to send PMs. To edit posts within the limits your forum level allows there is a cog to the right of your post. Clicking it will provide an edit option. How to reach member level:

https://en-forum.guildwars2.com/discussion/comment/118549#Comment_118549

Forum participants achieve "Member" level after just three days of participation and five posts. This means that those of you who joined us yesterday, with the launch of the new forums, will have unlimited forum edit rights Friday morning (Pacific time). Retaining a limit--albeit an increased limit--on new members is helpful because it aligns with our fraud protections, which actually have a 72-hour limitation on some elements related to account functionality.

Deleting posts requires a message to a moderator and a request to remove. If you don't want to do that you can edit the post and remove what you said and add something like [deleted] in its place. After the initial time editing restrictions you'll have unlimited time to edit.

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Be careful what you ask for. ANet might give it to you.