You can replace the SSD with a M.2 PCIe 2280 SSD. See crucial.com for compatible M.2 SSDs. Your current 32GB SSD is mostly like caching your HDD and your OS is installed on the HDD. I advise stopping the cache scheme which uses Intel Rapid Storage Technology (IRST) before removing the SSD. You will either have to reinstall the OS onto the SSD or clone/image the HDD, but either way, you will have to reinitialize the HDD before using it as additional storage otherwise you will have OSs on two drives and you will have to use the F12 Boot Menu to select the boot drive.

Also, since I am not sure how many PCIe lanes (1x, 2x, or most likely not 4x) your M.2 slot is. there may be no advantage of an M.2 SSD over an 2.5" SATA SSD.

The 32-GB SSD is only used as cache for Windows.

If you remove that 32-GB SSD, you'll have to clean install Windows on the new SSD. You won't be able to clone  the old HDD and migrate that clone onto the new drive. Before you begin, back up all your personal files on external media to be safe.

The new drive can be an M.2/SATA SSD or a SATA SSD.

Lots of threads about installing an SSD as boot drive in the XPS 8900, so search for them. Here's one to get you started.

There are a bunch of companies selling SSDs that are compatible with the PC model, like here.

Remove the 32 gig and clean install set to AHCI using F12 boot of OEM System builder dvd.

https://www.crucial.com/compatible-upgrade-for/dell/xps-8900

https://www.newegg.com/microsoft-windows-10-home-64-bit-installation-recovery-disc-only-no-license-key-included/p/N82E16832350237

Hi Ron

Many thanks for your reply and the link to the Crucial cards - this will ensure that I buy the correct type of card for the job.  However apart from the final advice about removing all other drives on 1st boot I found the other thread very confusing and not very helpful at all - I am now less sure of what I should be doing.

Best regds

Bob

Many thanks for the advice - I think I can follow the first bit but my lack of technical knowledge means that the last bit means nothing to me.  However even if it is not any faster than a regular SSD drive I think changing the card on the motherboard will make installation easier as I also have a 2nd HDD installed so connections should be easier.

Rgds

Bob

Thank you

Is it not possible to achieve this by creating a clone of the old drive?

Rgds

Bob

You should be able to clone your old drive. As I said before, you need to stop caching with the 32GB SSD before you remove it. After you clone your old drive to the new SSD, you will have to disconnect the old drive otherwise you will have to boot every time using the F12 Boot Menu to select to boot from the SSD. 

Thanks Vic384

These Rockstars seem to give conflicting advice - just wanted to be sure.

Rgds

Bob

@BBU77   - To be honest, I don't know when you clone a HDD with a cache SSD, if the cloned image includes what's cached on the 32-GB SSD.  And without that cached info, Windows won't work.

So you need to be careful here. If nothing else, back up your personal files from the HDD onto an external USB drive first to be safe.

If you reboot and press Ctrl-i at the Dell splash screen, does RST open and give you the option to break the cache? For the moment, don't do it, just see if the option is offered.