[C]Need help with deleting at head function in linked list

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Hello i have a program where i needed to add 3 functions to it.

sum up elements, insert at end and delete at front. The rest was already written from my teacher.

Now i could do the first 2 functions they are in bottom of the code but i dont know how i could do the last function.

the last function is under the main function i tried some shit but thats soooooo wrong.

Some text is on german but you should still understand everything

Pls help me 

Here is the code:

 

#include 
#include 

struct node {
int number;
struct node *next;
};

struct node *insert_at_head(int x, struct node *list);

void display_list(struct node *list);

int sum_up_elements(struct node *list);

struct node *insert_at_tail(int x, struct node *list);


int main() {
struct node *my_list = NULL;

my_list = insert_at_head(3, my_list);

my_list = insert_at_tail(15, my_list);

my_list = insert_at_tail(-4, my_list);

my_list = insert_at_tail(99, my_list);
display_list(my_list);
 printf("the sum of the elements: %d\n",sum_up_elements(my_list));
return(0);
}
struct node *delete_at_head(struct node *z){
struct node *current_node;
struct node *previous_node;
if(z==NULL){
 printf("Liste ist empty\n");
}
else
current_node=z;
z=z->next;
printf("%d got deleted",current_node->number);
free(current_node);

}
struct node *insert_at_head(int x, struct node *z) {
struct node *new_node = malloc(sizeof(struct node));
if (new_node == NULL) {
printf("Fehler bei der Speicherallokation\n");
return(NULL);
}
new_node->number = x;
new_node->next = z;
return(new_node);
}
void display_list(struct node *z) {
while (z != NULL) {
printf("%d ", z->number);
z = z->next;
}
printf("\n");
}
int sum_up_elements(struct node *z) {
int sum=0;
 for(;z->next!=NULL;z=z->next){
   sum +=z->number;
 }
 return(sum);
}

struct node *insert_at_tail(int x, struct node *list) {
struct node *new_node=malloc(sizeof(struct node));
if(new_node==NULL){
 printf("Fehler bei der Speicherallokation\n");
 return(NULL);
}
new_node->number=x;
new_node->next=NULL;
if(list==NULL) return(new_node);
struct node *head=list;
while(list->next!=NULL) list=list->next;
list->next=new_node;


return(head);
}