While in your library, when you hover over the thumbnail of a game, you should see an interface popup which lets you move them around or remove them. You can arrange them in any way you like until you are pleased.
Granted, that is not the same as a sorting function, and if you have a lot of games in the collection before you start organizing them, it may get tedious.
The things you own list cannot be rearranged, it will always sort the items you bought or claimed from most recent to least.