Converting to UEFI isn't as easy as just enabling UEFI.  The boot disc must also be formatted in "GPT" rather than MBR which is used with Legacy (NON UEFI) BIOS. Convert MBR Disk to GPT Disk in Windows 10 | Tutorials (tenforums.com)  
I have an older Latitude E5550, but I wanted to enable UEFI booting on it. It does have the option, but I know I am just not understanding something. When I open the BIOS and go to the "Boot Sequence" section, I switch the option from Legacy to UEFI. Then I have to apparently select the button to "Add Boot Option".  When I do this, what do I select? I can select a file name from drives FS0, FS1, and FS2, but I have no idea what file to select (FS2 is apparently my main drive with my data on it).  The system will not boot without me selecting a file because it says I have no boot device available when restarting.  However, when I switch it back to "Legacy" it works fine. Could someone please point me in the right direction?   Thanks.    
Latitude E5550 Adding UEFI Boot Option