Can I add more memory to my HP Stream 11-r010nr notebook?

The SSD is soldered as it is eMMC. The RAM is also soldered and most of these only include 2GB of RAM. You can get 4GB, but only on the Stream 13 - which is more expensive.

The problem with these systems was the Windows 8.1 with Bing licensing requirements - you can’t have more then 32GB of storage and 4GB of RAM - most only use 2GB of RAM to be compliant and meet price margins. Technically any type of storage works as long as the storage requirements are met from the OEM. However, eMMC is popular due to the low cost since these are disposable devices — even though they can use a M.2 SSD and if the user upgrades, that’s not on the OEM.
Note: Even then, these would only take SATA M.2 drives due to the chipset, but a M.2 2242 SSD like what they use in some Enterprise Chromebooks would work. 2280 may be too large for these, unless they did some clever engineering.
The other issue is these were meant to compete with Chromebooks, which is why they impose such requirements. However, it also is used as a OneDrive upsell. These Win10 Cloudbooks compete against in same market, but with better specs.

These 8.1 with Bing notebooks remind me of the Office 2010 Starter era when you could keep buying these every year for a new license, but the only difference is the offer is now a 1 year Office 365 license vs a lifetime copy. Office 2010 Starter only came with low end PCs (think Celeron, with barely any RAM) and was a direct attempt to sell Office licenses to remove the restrictions. Everyone who wasn't eligible did the right thing and bought it, and didn’t pirate the leaked Techspot installer. Right? Right? I hope you bought a legal copy in that case! /s

Due to the unique Microsoft imposed RAM and SSD limitations, they’re not upgrade friendly, and are basically disposable. However, the 2GB limit HP stuck to on these was due to cost reduction AND the Microsoft requirements, since they were chosen due to cost, and caution to not run afoul of what Microsoft required from this generation. These 8.1 with Bing systems are dead end.
Now I will give Microsoft credit here as much as this is a beatdown of how they directly generated millions of pounds of eWaste with the first generation. The 10 S devices can have up to 64GB and 4GB is more feasible than the older ones due to the allowances being improved this time around. In addition, the restrictions can be removed for free on 10 Home S devices. That was not possible with 8.1 with Bing’s search engine lock. Now the eWaste issue is on the OEMs, as many dump S Mode on laptops that only last 2-3 years due to being so low end.