how do I fix application memory on MacBook Air

Go to launchpad and type activity monitor. Launch this app and see which app is eating up your memory. I had this once when editing photos on my MacBook Air since that was the only computer I had. Turns out that the Airs hardware was simply too light for photoshop, so a good friend bought me an iMac instead for that kind of work.

But it can also be a memory leak, if you're aren't running functions that will use a lot of memory, You can also see that in the activity monitor