You might want to read this slowly, don't worry. It won't be that hard.
First, let's go with backing up your minecraft.jar file before you put mods, update, etc.
I do not own a mac so I'm not sure how you do these steps with it, please search in the internet on how.
Go to the Windows Start Button, here's a pic on how it looks
If you are on an XP, it should have a 'START' button.
Then, type in the search bar: %appdata% and press ENTER
You will end up with this
Click on .minecraft file, and you'll be welcomed by files, now, here's where it gets tricky.
1) Find the bin folder and click it, if you have no bin folder, try playing Minecraft and it will load it.
2) Find the minecraft.jar file
What is a minecraft.jar file? It's like a part of the body of Minecraft, without it, MC will not run properly.
It also shows you the kind of version MC is in, like 1.1, 1.2.5, 1.4, etc.
This is also where you put in the mods like Optifine, TMI, etc.
3) Right click it and click COPY
4) Go to your desktop and create a new folder and name it "MC Backups" or whatever you want.
5) Create another folder inside it and name it "Minecraft -insert version here-"
6) Paste the .jar file inside the "Minecraft -insert version here-" folder
7) Close everything and startup Minecraft
You are now able to update safely!
If you want to go back to the previous version, just open up your backup folder, copy the old .jar file, and go to %appdata%, then .minecraft, then bin folder, and then delete the new minecraft.jar file and paste the old one in. MAKE SURE YOUR MINECRAFT IS CLOSED WHEN YOU DO THIS OR IT WILL NOT WORK.
This is also useful if you install mods and you're not sure if the mod you'll install is compatible with your other mods so always backup your Minecraft.jar
Here is the 2nd way to go back to a PREVIOUS VERSION OF MC
Just watch this video:
Hope this helped! Enjoy!
