Welcome to forums !
1 - Right click avast! blue ball icon in your system tray. Choose Program Settings option. Click on APPEARANCE tab and in the right pane, choose USE TRANSLUCENT EFFECTS.
That is only if you have Windows 2000 or later. Earlier versions of Windows OS doesn't support these features, so if you have any one of them, you're stuck. You haven't mentioned anything about your system, and that's the first think eveybody should do when asking some question in forums like this (technically related).
2 - To switch between skins, go to avast! blue ball again, right click it and choose Start avast! antivirus option. When avast! is started, right click anywhere on the skin or simply press MENU button. Choose Select Skin option and you are good to go.
3 - resize your avatar please because it is way too big, actually I've never seen anything like that before. It looks more like desktop wallpaper than like avatar, lol. There are some forum policy and we all try to follow it. There is a button at the top of each page in this forum, called POLICY.
Cheers !
