You have to hold Command, Option (Alt) and R keys while your Mac is starting up. If you select Recovery HD, you will only be able to reinstall Mavericks. You should erase the hard drive in Internet Recovery.
I would recommend you to try to reinstall OS X Mavericks first, and if it doesn't work, downgrade to OS X Mountain Lion. I'm sure you can go back to OS X Mountain Lion
i hope my bootcamp is still gonna be there right?
I advise you to follow my User Tip instructions which includes cloning and baking up your BootCamp and other data off the machine and erasing the ENTIRE internal drive from Internet Recovery.
The reason for this is RecoveryHD partition restores the upgraded operating system version, not the one you want to revert back too.
If in the future you need to reinstall the OS X to fix issues, this can be a problem.
It's also possible Apple might have done changes in EFI and or the GUID partition map, which the reverted OS X version will be ill equipped to handle or fix if the need be.
With Apple it's all forward and no reverse, there are future changes, it's best to make sure everything is kosher and no half measures that can later cause issues.
Install everything fresh like it's a brand new drive, then nothing can go wrong.