So according to this

https://steamcommunity.com/app/573100

Tyranids have an extremely high winrate , im not very good at pvpbut i enjoy it and i think that this is due how good are their boarding skills, thats why i think that they should be nerfed a bit but in exchange they should get better guns, tyranid guns are pathethic and borderline useless and i ve seen some post about their guns missing point blank targets which is pretty lame.

How do you think that guns could be balanced? and why ?

There's a couple of reasons for this exceptionally high percentage. This applies for everyone of course, but there is a huge influx of new players who literally haven't played the game before. The global win rate should not be a determining factor for good game balance.

Another thing to note here is that Tyranids are high because they take advantage of two most broken mechanics of the game currently: Carriers and Boarding. Tyranids have the best of both current and with the most of their ships being severely overpriced, the competitive options that they do have are those two options, which kicks their win percentage up significantly.