[Q] rom,bootloader,kernels topic

Hello im currently using cm 12 and i would like to install lollipop with n4 style ... I found a ported rom and i tried to flash it and i got stuck on note 3 logo . i thought that the bootloader isnt updated from kitkat to lollipop is it possible ? Or the problem is happening from the kernel? Thank you ( ps if somebody could give a link to help my understand how kernel and bootloader works i would be thankfull )
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