I use Windows and want to switch to Linux, but I am confused with the installation. I need to install Linux in my C drive removing Windows from it without affecting other drives, how to do it?
Start from your USB thumb drive. Use the Try Ubuntu option as suggested before. After the full start you might want to make sure you are connected to the Internet first. You are going to need it for the installation. Next start the installation process.
This should be fairly self-explanatory up to the point where Ubuntu offers you to erase everything else and install it alone and like 3 other options. You will find an option ("Something else"?) that gives you the option to manually address the issue at hand. Usually the last one at the bottom. This option will take you to the list of harddisks and partitions.
WARNING: if you mess this up, you can lose your data.
But in this dialog you can make individual settings, as far as the harddrive goes. So, find your C partition. Mostly likely (BUT NOT GUARANTEED) /dev/sda1. Identified correctly, now tell it to put the mount point root or "/" there. And that will put the root file system there and install Linux on your C partion. Of course the C partition is going to be formatted and all former data will be gone, since Linux will use it's own, not a Windows file system.
Also make sure the boot manager is installed in the proper place.
If you use more than one operating system, make sure they are all either set up to use BIOS OR UEFI mode to start. Don't mix them.
If Windows was on your C partition before and given there is enough space on partition C, if everything is done properly, Windows (and everything else you had on your partition C before) will be gone and Linux is going to run from it.