Basics
How file/folder copying works:
This is an unfortunate problem that many people don't understand how file copying works. So try this exercise to better understand:
1. Create a folder on your C:\ drive called "test"
2. Add 2 text files there named "1.txt" and "2.txt"
3. Create a folder on your desktop called "test" also
4. Add 2 text files there named "3.txt" and "4.txt"
5. Copy the C: est folder and paste it on the desktop
What you THOUGHT would happen: 3.txt and 4.txt are deleted and replaced by 1.txt and 2.txt
what ACTUALLY happens: 1.txt and 2.txt are added to the desktop test folder. 1.txt and 2.txt are untouched.
Now, knowing that your life will be a lot simpler. So when you are told to simply upload the "admin" and "catalog" folders from the zip file to your store path, You don't need to worry that all your files will be deleted. Only the files that are there will be worked with... no more, no less.