Fine. So the 1st basic step to update a Station Board Pic or a Train Board Pic is to upload those pics in a normal blog and post it here. While uploading you have to keep in mind that the corresponding station/train/loco needs to be tagged. Once the blog posting gets over, you will find a button called "Actions", and it will be a drop down button. You have to take the cursor of your mouse there and you will find all the required options there: Add Train Board Pic or Add Station Board Pic etc.
Let me know, if you still find difficulties.