Sorry for butting in...
If its a mac , for write access you either need a) administrative privileges and/or b) need to be on the user account that created those files.
You can change the write access by ctrl+click on the folder and click on Get Info on the menu that pops up. after that, a window should pop up; under the ownership & permission it should say what you can do (read & write, read only, write only, no access). To change to read & write, you have to click on the down arrow and if there's a little lock next to owner, you should be able to click on the lock and change the owners name and the access that that person has.
I hope that's the right information. If not, listen to the experts =)
