Vostro 5090 SSD

I have a Vostro 5090 with a 256 SSD card and I want to put a 1TB SSD in. I had one Dell tech tell me that yes a 1TB will work and I had another that said that I can only go up to a 512 SSD. Which one is it?

I also have a 1TB internal SATA HD installed but am wondering if I should switch over to a 1TB SSD and if I can do that?

I am running out of space on the 256 SSD and yes I have all my documents etc saving to the internal 1TB hard drive or my external 1TB hard drive so only the software and operating system is running on the 256SSD.

Software I am using is Office and Adobe Creative Cloud, Bitdefender and some other software.

Also is it worth buying the SSD from Amazon and which SSD's should I avoid. I saw Crucial and that even told me I could put a 1TB SSD in.

Thanks