xcode6.3 - Xcode 6.3 not running iOS 8.4 - update to 6.4 fails -

i have upgraded ios 8.4, tried run xcode 6.3, asks can't mount device since it's running 8.4 version (".. running version of ios not supported version of xcode.") when try upgrade xcode 6.4 - update fails every time error message (try again using purchases).

any suggestions how solve this?

• delete /applications/xcode.app.
• download xcode 6.4 apple developer download site.
• mount .dmg , extract xcode.app /applications.