yeah man,
Take the 2 bolts our of the seat and remove the seat. Then look down and there should be your air filter.
There are a ton of threads on the internet about which filters, oils, rim grease, etc. folks prefer.
I am new to dirt bikes, I have had mine for about a year, and I use Twin Air filters because my personal opinion is that they seem to be of a little higher quality than the no-toil filters.
I use the no-toil oil and detergent as well as rim grease.
Get that filter replaced and keep'em clean
good luck
rtb