How do I convert my old Minecraft maps into the new format?

So basically, through a series of strange events, I have two world saves on my desktop, and Minecraft just went through the big Beta 1.3 update. Now I need to convert the old maps on my desktop to the new format that Notch has created. Will it do this automatically, or do I need to do it manually? Any information is appreciated, thanks!

 Ansver:

Hello, I was confused at first too but it was fairly easy to figure out:

1. Open Minecraft.
2. Click Single-Player.
3. Click the world you would like to convert.
4. It will do it automatically. (You may have to click accept or something)

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It does it automatically once you initiate it. First, paste them into your worlds folder in the .minecraft folder. In Windows computers, it should be in the appdata section, in the roaming folder since it can be played via desktop or web. This folder is hidden so you'll need to allow yourself to see them first.
Worlds can be renamed and have more than five now, so just make sure that no other worlds share the same name.
Then, once they're in Minecraft, just select them and try to play. They'll automatically convert.

So for the folder order: (your user folder)/appdata/roaming/.minecraft/world…
At least on Windows. If anything else, I've no idea.

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usually (at least in my case) select play selected world and it will convert automatically. this may take some time depending on the size of the file you wish to convert.

by "on your desktop" do you mean in a folder on your desktop or in the .minecraft/saves folder (if you have never moved a save file the second applies to you)

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At least in 1.3_01, you go to singleplayer, that choose the world that you want to convert, and at the bottom right hand corner of the screen, it will say "Convert world". Click that and after it loads, your done and the file will be converted!

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this isn't an answer, but i have kinda the same problem, i need some one to explain to me how to update my maps, because i updated them, but it deleted my whole world, so i restored it, now it won't let me play online and when i try to go to the minecraft website i only get a white screen, so i need to know how to update it again manually and easily

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It'll do it automatically, but you'll have to put the save files in the saves-folder. You can acces it like this.
User>Appdata>Roaming>.minecraft>saves

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Well i had some errors in the server console related to the world so I copied my old level.dat and replaced the new one and then the error was gone.