Upgrade 2009 iMac airport card?
The airport card is usually pretty stable.  You may want to start with the wireless router / air port.  You can pick one up at your local store and return it if it does not fix the problem.  As for the card itself it's replaceable but not really upgradeable from a quick google search.  If you have a free USB port you can use a Wireless AC USB adaptor like this... https://www.amazon.com/Edimax-Adapter-Supports-MU-MIMO-EW-7822ULC/dp/B01MY7PL10?tag=macworld05-20&amp;ascsubtag=US-002-3187363-001-1437949-web-20