Q: i can install the os x because the is "You need 4.95 GB of available space to download OS X Mavericks. Remove items from your startup disk to increase available space." however, my mac air his space . so how can i

When you select your boot drive in Finder, Get Info, it shows that you have more than 4.95 GB of free space?

If so, you might try emptying the Trash and maybe erase free space by using Disk Utility.

Freeing Up Space on The Hard Drive

  1. See Lion/Mountain Lion/Mavericks' Storage Display.

  2. You can remove data from your Home folder except for the /Home/Library/ folder.

  3. Visit The XLab FAQs and read the FAQ on freeing up space on your hard drive.

  4. Also see Freeing space on your Mac OS X startup disk.

  5. See Where did my Disk Space go?.

  6. See The Storage Display.

You must Empty the Trash in order to recover the space they occupied on the hard drive.

You should consider replacing the drive with a larger one. Check out OWC for drives, tutorials, and toolkits.

Try using OmniDiskSweeper 1.8 or GrandPerspective to search your drive for large files and where they are located.

In reality you will need a minimum of 12 GBs of free space to both download and install. Even then you still will need at least another 10 GBs free or a total of about 22 GBs.