Adam Bieber:
Right now, I am currently trying to master the first four jhanas but they always seem a little ambiguous like I cannot tell when I am in first or second or if I begin to meditate, I cannot tell which jhana I am in. I probably just need to keep practicing to lessen each jhana's ambiguity.
This is a common perception when practicing for mastering the jhanas. It has taken me several years of practice, strengthening my discernment, to be able to discern if or when I am in them at times. The best advice I can give when you're in this in-between stage is to not be too concerned with being able to figure out how you got "there." Just use the "there" as a tool to help you make progress on other fronts.
Being able to discern the different levels of the first four jhanas depends a great deal on how you entered them in the first place, what instruction you followed or if you just allowed the "current" to carry you along. By that I mean, were you aware of initiating changes as you transitioned from one to the next. If you weren't aware of the changes then don't fret about it. Just use the state to accomplish whatever work you set out to accomplish.
Generally speaking, they tend to be more discernible when you consciously go through each one, one at a time at the moment of initiating them. In its
samatha form, the fourth jhana is particularly distinct for its profound calmness and the stillness of mental movement combining with mindfulness and equanimity. From this point, simply inclining the mind toward a mental subject for study and examination (as in
satipatthana practice) will yield insight results.
Adam Bieber:
Can you be in the fourth Jhana without trying and then realize your in the fourth jhana? As you cycle throughout the day, do you change jhanas as well?
You are better off simply recognizing that jhana is just a more concentrated level of
samadhi. If
samadhi is "concentration" then jhana is
appana samadhi or "fixed concentration." It takes being able to attain
samadhi first in order to deepen it into jhana. If you can first sense the mind's having attained to concentration (uninterrupted attention on an object), then
appana samadhi deepens the mind's hold on that object. In that sense, then, the term "absorbed" may be perceived as being synonymous with the terms
appana samadhi and jhana.
When you "feel" or sense that the mind is "fixed" in concentration on an object, that's jhana. From that point, use it to discern the truths of the Dhamma.