Not able to switch branch

I want to switch branch from master to pravin_sep13 but showing error -

$ git checkout pravin_sep13
error: You have local changes to ‘lib/tools/portfolio_manager_tool.rb’; cannot s
witch branches.

1. On branch master
2. Changed but not updated:
3. (use “git add <file>...” to update what will be committed) #
4. modified: lib/breakout/staffing_alerter.rb
5. modified: lib/tools/portfolio_manager_tool.rb
6. modified: test/functional/spaces/documents_controller_test.rb
7. modified: test/functional/spaces/tickets_controller_test.rb
8. modified: test/unit/bk_util_test.rb
9. modified: test/unit/staffing_alerter_test.rb
10. modified: vendor/trac/templates/header.cs
11. modified: vendor/trac/templates/ticket_notify_email.cs #
12. Untracked files:
13. (use “git add <file>...” to include in what will be committed) #
14. app/views/spaces/documents/Copy of index.rhtml
15. public/images/Thumbs.db
16. public/images/admin/Thumbs.db
17. public/images/blue/Thumbs.db
18. public/images/clients/Thumbs.db
19. public/images/icons/Thumbs.db
20. public/images/li_hp/Thumbs.db
21. public/images/lpage/Thumbs.db
22. public/images/milestones/Thumbs.db
23. public/images/tickets/Thumbs.db
24. public/images/time/Thumbs.db
25. public/images/tools/Thumbs.db
26. public/images/tour/Copy of _chat.png
27. public/images/tour/Copy of _milestone.png
28. public/images/tour/Thumbs.db
29. public/images/wiki/Thumbs.db
    no changes added to commit (use “git add” and/or “git commit -a”)