Changing sidebar file through the browser.

Total noob to wordpress here. I was given the task of being the admin for our church youth group site. The sidebar section under editing of themes has links attached to it. One of the links expired and now has a search site with porn links. Help. I tried to edit the file and remove the link from the web browser, but it said that I have to change the permissions in order to save changes. I haven’t installed wordpress on my computer, I just access all the pages and admin through the browser. Is there a way to change the permissions and upload the changes from there? I don’t have any of the web hosting info, FTP tools, etc.