before u spawn and u choose ur kit, e.g. medic, there is a small arrow in a small box to the right of the kit (the one which u unlocked!) - if u press it it will rotate between ur unlocked weapon and the standard weapon.
When you are in the spawn screen, to the right of the weapons, in the top right corner of each weapon box, there is a little up / down arrow button. just press that and it will scroll thru your unlocks.
Be aware that servers have the option of having unlocks available. From time to time you might come across a server that doesn't allow unlocks. In this circumstance, your unlock selector (button with up/down arrows) will remain grey.
KJ
This, and all the previous posts kinda answer everything the OP asked about. Mod to close?