If you want o change the filename with the new content of your tags you can use
Convert → Tag - Filename.
This also gives you an immediate preview.
Build yourself a new filename with the placeholders of the tags, for example
%artist% - % %title%
It its not advisable to concentrate on filenames and only change them. You should rather see that you put your tag contents in order. "01 Dear Angie - Beatles" is definitely not a proper content of a title. The title in this case is "Dear Angie". Once you have your tags-contents in order it is very easy to build a new filename like shown above.
To update the contents of iTunes see here: