Anyone can contribute edits to OpenStreetMap, simply:
Sign up and login
Zoom in and/or search for an area
Follow the walk-through if it's your first time editing OSM
Search for a specific location (node) or street (way) you want to edit
Once your map is centred over the right area, hover around the area to find the right node or way to edit.
Click on the location you want to edit, or click the “Help” button for more info
Save what you edited, and you're all done.