Use UpdateView for two Django operations

I want to use a view to do two operations. From a list of articles I want to add or subtract the current quantity of the article.

I duplicated my view and changed the name to reflect the operation I want to do, I created 2 URLs with different names for each one linked to the view I want to execute. Despite this I still have the same field at the time of doing the operation (only shows the field to subtract the amount).

class Items(models.Model):
    nombre = models.CharField(max_length=250)
    descripcion = models.CharField(max_length=250)
    codigo_proveedor = models.CharField(max_length=250)
    categoria = models.ForeignKey('Categorias', on_delete=models.CASCADE)
    c_minima = models.PositiveIntegerField()
    c_actual = models.PositiveIntegerField()
    c_descuento = models.PositiveIntegerField(blank=True)
    c_incremento = models.PositiveIntegerField(blank=True)
    proveedor = models.ForeignKey('Proveedores', on_delete=models.CASCADE)
    carrito = models.ForeignKey('Carrito', on_delete=models.CASCADE, null=True )
    p_unitario = models.DecimalField(max_digits=10, decimal_places=2, null=True, blank=True )
    total = models.DecimalField(max_digits=10, decimal_places=2, null=True, blank=True)
    material = models.ForeignKey(Materiales, null=True, blank=True)
    tipo = models.ForeignKey(Tipo, null=True, blank=True)
    active = models.BooleanField()

    def save(self, *args, **kwargs):
        self.c_actual = self.c_actual - self.c_descuento
        self.c_actual =self.c_actual + self.c_incremento 
        self.total = self.c_actual * self.p_unitario
        super(Items, self).save(*args, **kwargs)


    def __str__(self):
       return '%s %s %s %s' % (self.nombre, str(self.categoria), str(self.c_actual), str(self.total))

views.py

# DESCUENTA ARTICULOS DE LA LISTA DE ELEMENTOS 
class CatItemUpdateDesc(UpdateView):
    model = Items
    fields = ['c_descuento']
    template_name_suffix= '_update_form'
    context_object_name = 'items'
    success_url = reverse_lazy('inventory:cat-list')


    def get_context_data(self, **kwargs):
        context = super(CatItemUpdateDesc, self).get_context_data(**kwargs)
        context['categoria'] = Items.objects.all()
        return context

# INCREMENTA ARTICULOS EN LA LISTA 
class CatItemUpdateInc(UpdateView):
    model = Items
    fields = [ 'c_incremento']
    template_name_suffix= '_update_form'
    context_object_name = 'items'
    success_url = reverse_lazy('inventory:cat-list')


    def get_context_data(self, **kwargs):
        context = super(CatItemUpdateInc, self).get_context_data(**kwargs)
        context['categoria'] = Items.objects.all()
        return context

urls.py

#HACE EL DESCUENTO DE LAS CANTIDADES EXISTENTES
url(r'^item_update/(?P<pk>[-\w]+)/$', views.CatItemUpdateDesc.as_view(), name='CatItemUpdateDesc'),

#HACE EL DESCUENTO DE LAS CANTIDADES EXISTENTES
url(r'^item_update/(?P<pk>[-\w]+)/$', views.CatItemUpdateInc.as_view(), name='CatItemUpdateInc'),

Any suggestions on how I can achieve what I want?