Fractured Axel

my first stunt kite i`ve build

after recent test flights i`ve decided to go for better lower spreaders (i think kite is worth of it), could you recommend me something,
do i need to change:
center-t (for sky shark)
2x Lowers Spreader (sky shark)
6mm solid carbon (for sky shark)

do i need change LE fittings?? (i have 6mm APA).

Normally you should have 5PT as lower spreaders and 6mm carbon for the other parts. You don't need to upgrade the spars as the difference will be minimum compared towards the cost.
You could however build a second kite that has more high end spars than 6 mm carbon (the B'zar 2010 would be a nice second self-builder)

Your Quartz flies well as it is, leave it like that (you'll be flying with this one for a long time coming!)