I've never heard of that title, but in general...
you have to acquire and carry the alternate weapons first before you can switch to them. And maybe in some titles, the weapons are not selectable if your ammo is empty for them... you'd have to find and pickup more ammo first. Just a couple of guesses you may want to check and verify.
how do i change weapons when playing hidden & dangerous 2? i have altered all keyboard controls to suit but still cannot change weapons at will. although i am new to gaming i really want to beat this game as i'm hooked already.

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