The memory is upgradeable.

https://www.dell.com/support/manuals/en-us/alienware-area-51-aa18250-gaming-laptop/alienware-18-area-51-aa18250-owners-manual/memory?guid=guid-479f06b6-06e9-4830-97bd-e52c074bada9&lang=en-us

@ejn63​ What exactly is upgradable in the laptop if you don't mind me asking?

The memory and drive(s) -- nothing else.  The CPU and GPU are soldered in so they cannot be upgraded (at least not without a mainboard change).

@ejn63​ Also one more thing, can I use Linux on it instead of Windows, the new update is wreaking the SSDs in computers, I don't want my new laptop to be wreaked.

I would not buy an Alienware system for use with Linux -- Dell has no support for it, and you almost certainly will lose features (the Alienware control software) by doing so.  While there is a Linux gaming community, the fact is that there are many games that are Windows-only -- so if the idea is gaming, Linux is likely not a practical option.  If it isn't  gaming you're after, there are plenty of other systems that would be better options at this price level -- the Precision mobile workstations or the Pro Max line among them.