typedef struct bul {
    float x, y;
    float direction;
    float velocity;
	int type;
    struct bul *next;
} bullet;

[...]

bullet *head = NULL;

main(){
[...]

bulletsUpdate(&head);

[...]
}

[...]

void bulletRemove(bullet **p) /* remove head */
{
    if (*p != NULL) {
        bullet *n = *p;
        *p = (*p)->next;
        free(n);
    }
}

void bulletsUpdate(bullet **n)
{
	if ((*n) == NULL) return;
	while ((*n) != NULL) {
		(*n)->y -= (*n)->velocity;
		if ((*n)->y > 1000 || (*n)->y < -1000) bulletRemove(n);
		(*n) = (*n)->next;
	}
}