Essays, information pages, and other informal pages that are only supported by a small minority of the community are typically moved to the primary author's userspace. These discussions typically happen on the page's talk page, sometimes with an RfC, but they have at times also been conducted at [[WP:MFD|Miscellany for Deletion]] (despite the MFD guidelines explicitly discouraging this practice). Other pages are retained for historical reference and are marked as such.
Policies and guidelines can be edited like any other Wikipedia page. It is not strictly necessary to discuss changes or to obtain written documentation of a consensus in advance. However, because policies and guidelines are sensitive and complex, users should take care over any edits, to be sure they are faithfully reflecting the community's view and to be sure that they are not accidentally introducing new sources of error or confusion.