Why would you want to do that?

A 2.5 inch SATA-SSD is much slower.

You just install the new SSD as D:

Yes you can, but as @Tesla1856 said, a standard SSD is not as fast as the M2 SSD. 

A couple thoughts on the approaches you could take:

I assume your original plan is to replace the M2 SSD the system came with so you'll have more space and can put everything on there (both the operating system (OS), applications, and your files). That's cool because you'll get the best performance across the board, but to keep the best performance you'd want to replace the M2 drive with another larger M2 drive and not the 2.5 SSD (although we're splitting hairs here, any SSD is a big improvement over traditional platter hard drives).

If you don't want to get a bigger M2 drive and then I'd follow Tesla1856's suggestion that you add the Samsung 500GB SSD as an additional drive. Then I'd save the M2 drive for the OS and the top few demanding or most frequently used applications, and put everything else on the 2.5 SSD. The only hassle here is that you have be sure when installing software or pulling in downloads to set the location to the new drive (D, E, or whatever letter you assign). You can change the default downloads location in your browser settings, and installing software directly or through clients like Steam, you'll need to take the extra step to likewise configure the install directory. If your system also has a traditional HD in it, you can save that for anything you want to archive, don't use as frequently, or don't need the best speed, like documents or media files. You'll have a lot of flexibility in this scenario, but you'll have to work to maintain the balance...lots of times when I install a game from Steam I forget to change the install directory and it goes to the C: drive or wherever the Steam client is installed.