Hi! I have installed LibreOffice 4.2 in my Linux Mint 16 and now i have 2 LibreOffice - 4.1.2 and 4.2. How can I delete the first? Thanks 
See L-user’s answer, below. I’m on Mint and had 4.1 from PPA; updated via PPA, and I only ever had one version on my system. How you remove depends on how you installed.
It really depends how did you install 4.1.2 and how did you install 4.2? It looks like you have installed LibreOffice 4.1.2 from official repository and 4.2 from some deb package (not from PPA).
Uninstall 4.1 using command:
sudo apt-get remove libreoffice4.1*
I am not a Linux Mint user, so I may be wrong. This is more of the question for Linux Mint forum: http://forums.linuxmint.com/ because it is Linux Mint specific question.
By the way I hope you understand that LibreOffice 4.2 is in DEVELOPMENT STATE and should be only used for evolution purpose and not for PRODUCTION ENVIRONMENT.
In case you would like to remove LibreOffice 4.2 then:
sudo apt-get remove libreoffice4.2*
In case you did something wrong and would like to remove ALL of LibreOffice programs (and after that install it back):
sudo apt-get remove libreoffice*
Remove Libreoffice from Ubuntu or Linux Mint?
Do not use sudo remove libreoffice 4.* that will leave you with a crippled system because files have to be replaced.
Here’s the right approach:
$ sudo apt-get remove libreoffice-core
$ sudo apt-get remove libreoffice-common
To remove the Libre configuration files
$ sudo apt-get remove --purge libreoffice-core