How to uninstal 5.3
Can you explain how you installed both versions? Did you use PPA additional to repositories or did you download from LO website? Or did you use installing in parallel?
What LinuxMint do you use (flavour like Cinnamon, LXDE, Mate, KDE; version: 17? 18?; 64-bit, 32-bit)?
You gave too little information for too big purpose imho…
I use Synaptic to manage my LibreOffice versions. There are other methods, but Synaptic gives a graphic view of the programs to be removed before you action them. On my linux-mint mate system you need to select libreoffice5.3, libreoffice5.3-ure and libreoffice5.3-debian-menues. Depending on how you installed your version, details may vary.
Thanks for your feedback, I managed to straighten the mess myself.