The 17 R1 has two bays for 2.5" SATA drives and it also has an mSATA SSD slot located under the palmrest. My guess is that you have a small 32 or 64gb mSata drive that is accelerating the old HDD using Intel RST. There are a few different SSD brands you can go for but something like a Crucial MX500 will do the job just fine at a reasonable cost.  It is pretty easy to install a new drive. There are two small screws holding the bottom cover on (not the ones fixing the nameplate). Remove these and slide the cover off. You will see the two 2.5" bays. The original drives will be held in by the HDD/SSD caddies. If you have drives in both bays then remove both of these and just install your new SSD. I would save any important data on your laptop to an external drive first just in case.  To reinstall Windows on the new drive you will need an 8gb (minimum) USB flash drive. This is a 'clean' installation so any programs or software you previously had will need to be reinstalled. Jump on another PC and go to the Microsoft Media Creation Tool and use this to download the Windows 10 ISO onto the USB drive. With the USB inserted in the machine, press F12 to get into the Boot Menu and select the USB drive. Windows will begin to install. You may get to a screen that asks you to upgrade or do a Custom Installation. Select Custom. You will then get to the point where you select the drive to install Windows on. Since you removed the old 2.5" drives, you should only see one option but it could also show the mSATA. If you buy a 500gb drive then one of the drives will show roughly 460gb free space. Select this drive and hit next. Windows will now install on your SSD. Once it installs, the system should now recognise your SSD as the main boot drive so if you had a single 2.5" HDD in the laptop before, you should now be able to reinstall it and get your data back. Windows will still be installed on this drive but you can delete all the Windows files if you like.  If the system tries to load Windows from the old HDD then you need to go into the BIOS and set the Boot Order to select your new SSD first.   
For some background, I have a 2014 Alienware 17 R1 Laptop. And for the past couple months, I’ve had a lot of problems with the HDD (1TB) always running at 100% and the computer would slow down a lot. I tried many fixes and they would only bandaid the issue, not too recently though, I would have a blue screen error (REFERENCE_BY_POINTER) happening like every 15 - 30 minutes on the computer. I have tried everything and I’m convinced I just need to replace the old HDD with a new internal SSD. My only problem is, I don’t know what SSD in particular I need to use to replace in the computer. I have seen ones that look like small NVME / SATA chip forms and ones that look like bigger Square box looking ones. All I really need are some SSD recommendations (500 gb preferably) and, if you know one, a disassembly/assembly video only if you have one. As my username says I’m fairly new to this, so any and all help is appreciated 
17 R1, upgrading from HDD to SSD