Most users here are in the US or UK and may not know what options exist in Norway. OWC/US shows RAM for that iMac model
https://eshop.macsales.com/shop/memory/iMac/2010/DDR3_21.5_27
AND has a partner in Norway. Try this:
https://www.matrixproaudio.no/categories/owc-other-world-computing
OWC also has partners in most other European countries:
https://www.owc.com/partners/where-to-buy#map
NOTE: A 2010 iMac must have an Intel i5 or i7 processors to use more than 16 GB RAM.
⚠️ However, if your iMac is slow, the most likely cause of slowness in that model is the hard drive, not RAM. Adding RAM will make no improvement if you have the entry-level mechanical hard drive. As the 2010 iMac has but a slow 3GB SATA drive bus, there is no better drive option other than installing an internal SATA 3GB SSD.
We can neither see nor touch your computer in this setting. If you wish a data-driven evaluation instead of the general conditions I stated, please post a s system configuration report. Fortunately there is a safe, secure way to do that without our playing a protracted game of "20 Questions" that could go on for days or longer
We can quickly and within the very limited confines of these forums help you determine what issues are at play if you use EtreCheck Pro, available here:
https://etrecheck.com/index
The free version will do nicely for this purpose, although the app is worthy of our financial support.
We can see hard data about drive performance, software issues, and RAM usage. Etrecheck is the development of a long-serving and trusted contributor here expressly for displaying information in these forums to help us help you by remotely evaluating Mac issues. It will not reveal any personal or secure information.
Please see this excellent user tip on how to post long text reports like EtreCheck's into a forum response:
How to use the Add Text Feature When Post… - Apple Community