Geograph - photograph every grid square

Use the 'Upload a larger size' link on the photo (or edit) page and submit the size you want (or select the preferred option on the page). This will overwrite the original selection although there may be a brief period when the originally selected size will be available due to caching and the wait before approval.
Be aware that if the very large version has been on the site for a while it may already have been downloaded from the site as a CC licensed image.
Note: if you did not want to license a larger size at all you will need to go through the same process but using an image marginally larger than 640 pixels wide (641 is enough) in order to remove the larger size options.

By uploading an image to Geograph, you agree to license it under a Creative Commons licence. This allows anybody to use your image for any purpose, including commercial use, as long as they give credit to you. They don't have to ask your permission before doing so.

The standard 640x640 pixel size is too low resolution for the vast majority of commercial uses, and it is not uncommon that Geograph-ers are approached by publishers or the media for a higher-resolution version for printing. If you agree to supply one, you can ask for a fee if you like. Basically, you're granting them a separate licence to use another (higher resolution) image. It is up to you to negotiate the licence terms and remuneration you want.

Of course if you choose to license a higher-resolution version under the CC licence alongside the standard size picture, then people are free to use that as well.

Many Geograph-ers are happy to give high-resolution versions for free for charity or community publications while charging a commercial fee from other organisations. Commercial providers of education (materials) seem to be a borderline case for many.

If your friend asks you to and for some reason cannot create their own account then that's fine provided they understand the Creative Commons licence. You should credit them as the photographer when submitting.
See related article: Photos not taken by submitter

The simplest method is to overwrite the large version with a smaller one.
This only needs to be one pixel larger than the displayed image (641 pixels on longest side) but can be whatever size you are comfortable to licence for reuse.
Just click on the link [Upload another large version] and follow the steps on the page.

This process works best on unmoderated images as these will not yet have been picked up by others (wikimedia, British library, site visitors etc). We cannot guarantee that images overwritten after moderation will not have been copied elsewhere before being replaced.

If you have taken the picture yourself, or you have inherited it from a deceased relative and are certain of the copyright history, the age of the photograph is of no consequence.

With regard to old postcards or photographs without provenance, although the photo may well be out of copyright it is incompatible with the Creative Commons share alike licence and cannot be accepted on Geograph.

If you have taken a current view of the same place and would like to link it to the old photograph you can submit the recent shot here and upload the old photo to the media repository http://media.geograph.org.uk or a photo-sharing site like Flickr and link to it there in your description.