Delete a record in struct using free ()

I am creating a registry using struct , where I should have a menu to include, display and answer (exclude) patients.

The problem is in the delete function that because of my lack of knowledge I do not understand what the correct way to do it would be. I thought about using free() but for dealing directly with memory I'm not sure if it would work in all cases.

    #include<stdio.h>
    #include<stdlib.h>
    #include<string.h>

    char menu(){
        fflush (stdin);
        printf ("\n\t\t-----Menu-----");
        printf ("\n\t\t 1 Incluir Paciente");
        printf ("\n\t\t 2 Mostrar Pacientes");  
        printf ("\n\t\t 3 Atender Paciente");   
        printf ("\n\t\t 0 Sair");
        char op = getch();
        system ("cls");
        return op;
    }

    typedef struct paciente{
        char nome [20], matricula [6], senha[6], atendimento[50];
        struct paciente *prox;
    }pacienteat;

    pacienteat *ini, *aux;

    void inicio(){
        ini= NULL;
    }

    int estaVazia(){
        return (ini==NULL);
    }

    void inserir (){
        int senha=1;

        aux=(pacienteat*) malloc(sizeof(pacienteat));
        printf("\nInforme o numero do atendimento");
        fflush(stdin);
        gets(aux->atendimento);

        printf ("\nInforme o nome do paciente: ");
        fflush (stdin);
        gets (aux->nome);

        printf ("\nInforme o numero da matricula: ");
        fflush (stdin);
        gets (aux->matricula);

        printf ("\nInforme a senha atendimento: ");
        fflush (stdin);
        gets (aux->senha);;

        aux->prox = ini;
        ini = aux;
    }

    void listar(){  
        for (aux = ini; aux != NULL; aux = aux->prox){
            printf("\nNome: %s - Matricula: %s - Atendimento: %s - Senha: %s", aux->nome, aux->matricula, aux->atendimento, aux->senha);
        }
    }

    void excluir(){
        int n_remover;
        listar();
        printf("Digite o numero de quem voce quer remover");
        scanf("%d",&n_remover);
        aux[n_remover] = aux[aux->atendimento-1]; 
        atendimento--; 
        aux = (pacienteat*) realloc(pacienteat,num*sizeof(pacienteat));
    }
    int main(){
        inicio();
        int x=0,nn;

        char op=menu();
        while(op != '0'){
            switch (op){
                case'1':
                    inserir();
                    break;
                case'2':
                    listar();
                    break;
                case'3':
                    excluir();
                    break;
            }
            op = menu();
        }
        system("pause");
    }