I have downloaded the xcode5_GM_seed and install it, but I cannot find iOS7 simulator in components.
Where can I find iOS 7 simulator?
XCode 5 comes with iOS 7 sdk and simulator automatically. However, since iOS 7 is not supported in old "iPhone" and supported in "iPhone Retina..." and "iPad.." so you need to select appropriate iOS simulator in your project... (your old/existing projects seems to be selecting to "iPhone" simulator)