How do I change my location?
There are different answers depending on which location you are referring to.
The location of posts you see on the main posts page is based on the groups you are a member of and your post settings. You can add and remove groups on the Groups page at any time. And you can change your post settings using the post options on the Settings page.
If you're trying to change the location description that shows up on your posts, you can only change this for new posts. Every time you post, there is a Location text field on the New Post page that controls the location description that will show up on your post.
If you're trying to change the location displayed on the map that goes with your post, simply click the link next to the map that is labelled "Wrong location?" to correct the location. This will only update the map display and so it should only be done when the map doesn't match the location described in the text of the post.