You cannot change them back. Its a poor joke mojang has pulled on its minecraft players, that theyve changed all skins to villager skins.
If you dislike the crappy Villager skin (Misplaced head and not nice at all) you can block it and get default Minecraft Steve.
To do that on Windows you need to change the hosts file, and basically route the call to the Minecraft server to nowhere.
The file is in C:\Windows\System32\drivers\etc and is just called "hosts"
Open that file in a text editor of your choice
In there you add this line at the end: 127.0.0.1 skins.minecraft.net
That will tell Minecraft that the server for the skins is located on your computer which it isn't so it gives you default Minecraft Steve back.
Naturally once this 1st April crap is done, you will of course have to remove that line anyway to get your skin back.
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