If you want to change the wplms directory name, then you have to make 2 changes:
1) In the wp-content/themes/wplms rename wplms folder (which I guess you already tried).
2) Now you need to open the theme and go to inlcudes->config.php file. Now change the VIBE PATH, refer: http://prntscr.com/cxf8g7PS: You won't be able to get automatic updates of wplms theme if you do so.