You have to go into an FTP program and retreive the files to be edited. You can find them here:
/public_html/wp-content/themes/classic
OR
/public_html/wp-content/themes/default
You can then overwrite the files with your edits.
That’s the most secure way (downloading, editing, uploading), but you can also just CHMOD your theme’s files so that you can edit them via your admin area. Be aware that if someone compromises your site, they’ll also be able to edit your theme, so…
http://codex.wordpress.org/Changing_File_Permissions
I feel the best & safest way is updating through ftp. Bco’z you can incorporate changes offline without any hindrences and safely upload after completion.
Online editing is good for making just a bit of small changes, which needs immediate attention and one doesn’t have time to edit/upload.
Rest is the choice.
thanks very much for your help.