Replacing the hard drive with an SSD will make your system much faster and more responsive, a noticeable difference and the most bang-for-your-buck that you can get for any upgrade.  Any of the major brands, (Crucial, Samsung, WD, etc.) will be fine. I've used Crucial MX500 2.5" SATA drives to upgrade a couple of old computers, and I'm happy with them. Crucial recently reduced their pricing, so you can get a 1 TB for around $50 and a 500 GB for around $35. There are web sites that test and compare various SSDs, but for 2.5" SATA really any major brand will be good. If you want to extend the life of your drive and improve performance, you can set aside some unallocated space as Over Provisioning. I use about 6% of my 1 TB SSD as Over Provisioning, but you can choose more or less. There are many tutorials about this, and the "best" number for you varies according to the intended use of the drive. Whenever touching components or working inside a computer, wear a grounded wrist strap, also called anti-static wrist strap, ESD wrist strap, or ground bracelet. It's a cheap and sensible precaution. Rest the laptop on an anti-static mat or at least a reasonable alternative such as corrugated cardboard. (Repeatedly touching a metal case part is not sufficient mitigation with modern components.) You could do a full image backup and restore it to the new SSD, or a clone (which is less safe, but can also work). However, if you've had the current installation for some time, I would prefer to clean install Windows to the new SSD after it's installed. I wrote a detailed Windows installation process that may help you. And here's another description of the install process, from a Microsoft MVP.
About the only thing I have done to this Dell 3847 is to upgrade to 16GB RAM. Now I want to replace the HDD with a SATA 500GB 2.5 inch SSD to entend its potential life (and help speed up boot). There is only 178 GB used on current drive, so 500GB should be more than ample. Is a Samsung 860 EVO good to use? If not, recommendations please. What do I need and how do I do it? I do not want to keep old HDD as a backup, I will replace it with SSD. Thanks for any help you can give.
Upgrading Hard Drive on a dell 3847 Desktop