imac not staying connected to wifi
Hello, I am running a mid-2010 21.5 inch iMac and attempting to run it wirelessly to my wireless router / modem. OS is Yosemite 10.10.1. Once connected the iMac can access the internet normally, send mail etc, however, sometimes (not always), after going to sleep and I start using it again, I find that it has lost, or does not maintain, or does not re-establish the wifi connection. Comments please. Are there some setting changes I should try. I've found nothing obvious to try.
iMac (21.5-inch Mid 2010), OS X Yosemite (10.10)