Hi, welcome to justanswer.com! My name is Mike.
I will need some information before we begin:
Please go to the Apple logo at the upper left of your computer screen to About This Mac and give me this information:The exact system Version (listed right under OS X ??)ProcessorMemory
Apps or Photos etc.. won't bog it down unless you have them all open t the same time
Hi there and welcome
As the first step, remove the power to your wifi router, wait 5 minutes, then connect the power and restart the Macbook Air
Let me know how it then performs.