There are lots of KDE packages available in Synaptic Package Manager. I don't know enough to recommend which ones you need but know enough to recommend you not try to change the DE on Linux Lite since it is designed to use XFCE. If you don't know how to Synaptic and/ or how to find out what packages to use, you are not ready to try changing Desktop Environments. I recommend you save your home folder and install Linux Lite 3.4.