Q: I have version 10.105 trying do upgrade to El Capitan. does not want to download. system search runs continuiously

Check for application compatibility

http://roaringapps.com/apps

How to upgrade?

Section: "Upgrading is free. And easier than you think."

http://www.apple.com/osx/how-to-upgrade/

Backup the Mac before upgrading.

Best.

Hi Sorayah, what do you mean "system search" runs continually? If you mean Spotlight, have you tried rebuilding your Spotlight index?

Rebuild the Spotlight index on your Mac - Apple Support

If it is not Spotlight, then please explain more fully.

Try downloading in the Safe Mode or another admin account.

Safe Mode - About

Safe Mode - Yosemite