If i train a lot at zone 2 will TR increase my upper zone 2 numbers in line with my new level of fitness?
Sort of.
TR calculates your Z2 boundaries as a percentage (55% - 75%) of the FTP it holds for you.
So presuming that percentage is accurate for you and presuming that you retest or allow TR’s AI FTP to adjust the FTP as it sees fit, then the boundaries will move in line with the changes to your FTP.
A lot of people use HR to judge their Z2 rides. If you choose to do that, you can use the power change buttons on the workout player to help keep you in your target HR range if that is needed.
Also consider what you want to get from your Z2 training. A 60 minute Z2 ride right at the top end of your Z2 is very different from a longer ride where you hold a zone 2 power level until you reach the point in time where you can’t sustain that power without your HR climbing up through the top your Z2 HR range.
Lots of fun to be had.
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Also, if what you’re really after is being able to do your Z2 ride a few watts higher, turn off erg mode and then you can ride at whatever wattage you want.
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As @ivegotabike mentioned, we base all of our power zones off of your FTP, so as your FTP changes, we’ll adjust all of your training zones, including zone 2.
These are estimations though, and each of our LT1 (~high zone 2) is likely a slightly different percentage of our FTP.
This is where heart rate can come in handy as a guide to use alongside power to help dial in exactly where you should ride in that zone from one day to the next.
Additionally, your Progression Levels help us hone in on your capabilities in each specific zone and prescribe workouts based on them which helps us keep your workouts really accurate beyond just your FTP. 
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