Q: how to delete others from start up disk so that i can make some space for installing new os.?

Go step by step and test.

1. Start up in Safe Mode.

    http://support.apple.com/kb/PH11212

2. Empty Trash.

   http://support.apple.com/kb/PH13806

3. Disk space / Time Machine ?/ Local Snapshots

  Local backups

   http://support.apple.com/kb/ht4878

4. Delete old iOS Devices Backup.

    iTunes > Preferences > Devices

    Highlight the old Backups , press “Delete Backup” and then “OK”.

    http://support.apple.com/kb/HT4946?viewlocale=en_US&locale=en_US

  5 Re-index Macintosh HD.

     Spotlight reindexing will take a while to finish.

     System Preferences > Spotlight > Privacy

      http://support.apple.com/kb/ht2409

     If you don’t have Macintosh HD icon on the Desktop:

     Finder > Preferences > Sidebar

     Enable Hard disks under “Devices”.

6.Try OmniDiskSweeper. This will give the storage size details of the items.

       https://www.omnigroup.com/more

   Select Macintosh HD and click  “Sweep Selected Drive” at the bottom.

   Delete the files yo don’t want to keep.

   Be careful. Delete only the files that can be safely be deleted.

   https://www.omnigroup.com/more

7. Move iTunes, iPhoto and iMovie media folders to an external drive.

      iTunes

      http://support.apple.com/en-us/HT201562

      iPhoto

      http://support.apple.com/kb/PH2506

      iMovie

      http://support.apple.com/kb/ph2289

It will help you immensely if you understand what the OTHER category is.  Please read this:

http://support.apple.com/en-us/HT202867

Do not think that files in that grouping are irrelevant or minor.

Ciao.