I assume you would have back up of all your data.  Using Windows Creation Tool to make a USB and just perform a clean install of Windows 10 and deleting all partitions from both drives during installation.  Select SSD to install, let Windows create and manage boot option (Windows Boot Manager).  When the Windows installation is complete, install the machine chipset driver, then the Intel HECI driver, after that let Windows update to install the rest.  You can go to Disk Management and set hard drive as data drive.  Go to Windows storage option and set new apps on drive C, all other (documents, downloads, music, pictures, videos) will be on drive D. Don't forget to set SATA mode to AHCI and enable UEFI in BIOS prior to installation.
Hi last night I tried replacing my 1tb HDD with a 250gb Samsung 870 250gb evo SSD yes I know it’s small but I only want it for windows wont be putting anything else on it an was going to use the HDD as the storage device so I installed W8.1 that came with my pc onto the ssd worked fine but now I have a dual boot machine can pick SSD W8.1 or HDD W10 the HDD is 10 from the free upgrade when they offered it an I cannot make the SSD the bootable device in bios it doesn’t show there but does show under SATA an I cannot format the HDD I am now stuck with the dual boot if I unplug the HDD I get a black screen with No bootable devices found but as soon as I plug it back in I get the blue screen after startup where I can choose which device to boot from but now for some reason only the SSD W8.1 will load to desktop the HDD ask for repair think I deleted windows files by mistake I do get the option to restore it but when it asks me for the password for the Microsoft account it says password is incorrect when I know 100% it is correct kinda at a loss now any help would be appreciated 
HDD to SSD an SSD not showing in bios to make it the primary boot drive