How to upgrade RAM?

Thanks.

Here is image link on Google Drive: https://drive.google.com/file/d/15P6PX0IvmSgCj8CIWP6CSCpZaFIue9__/view?usp=sharing 

@VAer We can't see your image yet until it is approved by the moderator. I suggest you look at crucial.com for guaranteed compatible memory and fairly good prices. RAM should be installed in matching pairs and Crucial memory is usually compatible with existing memory if you install it in matching pairs. If your 16GB is a single memory module then you may have a problem. It is always helpful to post the model and other information about your computer here when asking for help.

As far as whether CPU or RAM is more important for excel calculations it depends upon the size of the spreadsheet and the type of calculations you are doing. For example, if the calculations are chained, that is, if the value of a cell depends upon the calculated value of another cell throughout a large spreadsheet then CPU speed is very important. 

@VAer We cab see your image now. It appears to be an XPS 8950. This link will help answer your memory question: https://www.dell.com/community/XPS-Desktops/XPS-8950-future-RAM-upgrade/m-p/8143581

With regard to your spreadsheet question, that is hard to answer without knowing more about the spreadsheet you are working with. 

I think it is XPS 8940, not XPS 8950 (which should come with 12th generation CPU).