I want to download music that i bought using one device onto another. I use the same apple account. Have change the email that is assosicated with it, but that should not matter. But no little cloud appears besides songs that I have bought. Why?

You are in a country where music can be redownloaded (it's not possible in all countries), you haven't changed countries since buying them, and they don't show in the Purchased tab in iTunes store app on your device, or the Purchased link under Quicklinks on the right-hand side of the iTunes store homepage on your computer's iTunes ? If not then are they hidden : http://support.apple.com/kb/HT4919

If you aren't in a country where music can be redownloaded then you will need to copy if over from the device or computer that it's currently on.