Such measures might not be necessary if the site allows you to make corrections or deletions after the fact or does not permanently disable access to your work or comments. Unfortunately, many sites deny access after the fact completely and forever as a penalty for being BAD.
Here then is the means to address a situation in which you want to delete your material and comments but the site has disabled your access. A DMCA Take Down notice includes copies in "unpublished" sections where other users can continue to post comments and replies and receive links to your material by email, even though the material is in the "unpublished" section. Sites must comply in deed and not just words or suffer the consequences of their resulting copyright violation.
Step 1: Gathering the necessary information
The name of the Instructables DMCA agent for instance is:
1467 Park Ave
Emeryville, CA 94608
Normally the phone number which is provided for the DMCA agent is a fax number, but if it is not then you can send a certified letter to the snail mail address. Note that a picture is not necessary, although a likeness or avatar might help the site's staff connect the name with the person...