Finally got the solution to remove the themes from N73.When I googled the topic I got many solutions but no one was complete. The problem was removing theme that are not shown in application manager.
There is solutions that going in to “\private\10207114\import” located on memory card and delete the folder named like “51879ad856c3d0ed”each folder refers to a theme, but the problem is that many themes in the folders are not saved by names but by strange numbers like ” 22c32c2c5345634d”.
If you want to delete seleted themes here is the solution.

1.Goto TOOLS then select THEMES the select the theme you want to delete select EDIT the theme and go to Power Saver click it and select TEXT enter a text like “enter any word” (enter what ever you want), then OK.
2. Connect your phone to the PC in MASS STORAGE mode. In WINDOWS go to TOOLS then FOLDER OPTION then VIEW CHECK SHOW HIDDEN FILES AND FOLDERS.
3.Browse your memory card and Navigate to folder “\private\10207114\import”, there are many folders and in each folder there are 4 files with extension *.ini , *.mbm, *.skn and *.mif, *.ini files can be opened in windows others can not.
4.Now the most tedious job open each folder in “\private\10207114\import” and open *.ini files
This file contains only one line which shows your POWER SAVING settings at the end of the line if there is a entry like ” ScreenText=The Word you entered ” (without quotes) then this is it delete the folder in which you got this file.
You are Done.
This is really tedious but these works for sure.
Thanks
Ps: SORRY FOR MY BAD ENGLISH.