How to convert legacy installed windows 8.1 to uefi mode

so as the title above,i recently reinstalled my laptop's windows 8.1,during the installation the boot manager doesn't show my installation media because im in uefi mode,so turned on launch csm and can boot from my installation disc,during the setup,the windows cannot install on gpt disk problem appeared,so i converted it to mbr by using shift+f10 method,installed windows 8.1 and now using it but now when i goes back to bios and disable csm which is enabling uefi i assume?,windows did not boot and goes straight into bios,means in uefi mode it didn't load my windows since i've installed my windows on legacy(pls spare me im a newbie not really knowing all these crap about uefi and legacy,like if you install windows on legacy you can't boot it in uefi mode anymore which make sense but i never know this) so saw some thread on how to convert legacy to uefi withoust lost of data,but im not quite sure i understand how to do it, so i want to ask if anyone could help me on this issue thks

i know this might have been discussed many time ago,but still i wish to convert it and since uefi boots faster,and also just wanted to revert back to how my laptop was before which is windows 8.1 preinstalled in uefi