Unity3.0 deleting assets

hello,i want to download the latest version of unity. but when my friend downloaded unity3.0, it deleted his old unity and all of his assets in that unity. so is there a way to make sure it doesnt delete my games and all my assets or a way to preserve them? Any help is greatly appreciated!

Downloading Unity doesn't delete any of your assets or projects. The only thing it does is overwrite the previous Unity installation, unless you rename the folder for the old version, in which case it doesn't overwrite anything at all.

If by deletion, you mean the objects disappeared from the Scene, then you need to reimport the assets/ add the meshes to the gameobjects in the Hierarchy menu again to bring those objects back on the screen. When you convert a project from Unity 2.6 to Unity 3, there have been cases where the linkage has been broken.

Always make a backup before upgrading Unity.