To install Mavericks, you need at least 2 GB of memory and I only have 1 GB. Can I load more memory?

Yes, you can, though you'd need to tell us your exact model of iMac before we could tell you specifically what memory you will need and how much you can expand to. There are a number of good vendors; I've used Crucial and Other World Computing (OWC). Both have been of high quality and good service, and either can tell you exactly what you'll need for your iMac. Other folks here may have additional vendor recommendations.

I'd definitely recommend expanding beyond 2GB. It won't cost that much more and your performance is almost sure to be better than if you just get the minimum 2GB.

Regards.

That model of iMac can recognize up to 6GB of RAM. I'd suggest 4GB: price for that will be around $72.00 US. Give Crucial, OWC or any other reliable vendor your model information and they'll get you the correct RAM for your system.

Regards.