will you need to rejet for a half system and if so does anyone know what jets i need

118/120 is a good base setting.

yes, in most cases with fitting an aftermarket exhaust half system you will need to rejet the carbs.
Sizes depends on what mods are done to the engine.

none, engine is standard .

In that case I agree with Viper_biker, go from a solid base (118/120 is good).

And 2.5 turns out on the a/f screw and you should be in a good 'ball park' area for the bike. Any biggeron the jets and you'll find yourself being a bit rich. I ran 120/122 on my bike with an Ethos half and that was too much even with 2 sheets of HRC filter foam which would be petting more air in.

I ran a half Ethos system (since changed end can to Tyga) with 118/120 jetting with needles raised and it was far too rich. I had the type of can with the three internal sections and small outlet bore which causes major restriction and gives a whiney type sound.
I kept the ethos pipework and put a Tyga open can on to help lean it but ended up reducing the jets to 115/118 and no needle shims.