with Fedora 21 I have been using the standard Fedora release, but, if you do not, I think that you can remove the existing using yum...
Is it installed?
yum list installed | grep "libreoffice"
I expect that you can remove it using
yum remove libreoffice*
I have always used "yum localinstall *.rpm" to install the RPMs after I extract the code.
Last time I did this, there was a GUI integration driectory under the standard RPM directory. I changed to that directory and installed the RPM meant for UI integration for gnome. I don't remember what that is called off hand, or even if it is still required. I don't have time now to download and check the RPMs, but, if you send a list of RPMs, I can tell you which one it is.