Im lieutenant and I cant switch ships, or discharce my first one, its greyed out.
It says its set as my current. How do I unset it?
You unset by picking another ship and setting that one as current. You always have to have one ship as your current ship. In other words, you don't have a desk job, the only way to leave one ship is by transferring your command to another.
Relatedly, how many ships are you allowed to have? I'm at Tier 3 and am not yet at the point where I feel it necessary to decommission ships. I even have 2 T2s because I purchased an Exeter from the zen store after flying my free T2 around for a while. I keep my older ship's systems upgraded when I can, and use them to store devices I may wish to try later.
When you rank up, the game always gives you another ship slot so you can claim your next free ship without discarding anything. The only reason you'd need extra slots at that point is if you claimed your free one, then bought a different one off the C-Store and wanted to switch. Even then though, my recollection is that you always have at least one extra slot, so that you could buy the Tier 1 ships (Connie, NX or Oberth) and not be stuck in a position where you can't claim them. Been a long time since I had a free account though, memory may be fuzzy.