You don't have trusses, they are rafter. That vertical member is odd. Guessing it was added at some point to deal with sagging on the tie.
Those horizontal beams are there to stop the walls from spreading. Moving them as high as you show probably won't work.
Where are you located? Please add it to your profile. Helps other advise so we know if you have to worry about snow, hurricanes, etc
Collar ties are horizontal going from rafter to rafter.
https://images.app.goo.gl/P8HhMvKdSBwruubTA
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There appears to be already a couple missing from the two rafters on the right. A little odd. I wonder if the verticles were put there so the 'ties' could have been used for some storage by someone before that sorta knew better but figured he was gonna be light enough with the load?
the last time I had a conversation with a code inspector I was told that the collar ties need to be in the bottom third of the rafter( height wise).
