Pointer to managed pointer

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C++

Hello everybody. I have a problem with allocating system::drawing::bitmap in function.

void image_warp::preview(Bitmap ^ newpic)
{
    if(newpic!=nullptr)
        delete newpic;
    newpic=gcnew Bitmap(pic_processed);
}

bitmap is allocated and "usable" in function but when app skips back to main it is not allocated anymore. Of course I would use "&" in simpler times but seem that it does not work for managed pointers. I tried some google-ing but struggled to get any help. I know that the solution is simple but I have no idea what the correct syntax is. Thanks in advance