Thanks for playing!
You can see which ammo a gun uses in the tooltip, but they are pretty confusing and I am right now in the process of redoing the tooltips. I believe it will be easier to tell.
A lot of the upgrades are a bit undercooked at the moment, especially for laser type guns. Increasing the spread of the laser will cause the beam to go in a different direction every frame. The spread is so small on it that its not very noticeable unless the spread is increased a lot by a flat amount. Having it change AoE would be much better though...
If you can apply an upgrade to a gun it will also affect it, unless I've made a mistake. Increasing the range will increase the laser range too.