Go through this link:

https://www.odoo.com/forum/help-1/question/how-to-change-the-values-for-a-selection-field-72934

If your selection field is static list of tuples defined in field, then there is no way to do. If it is a method or global variable you can change it.

Hi, 

You can follow following link for this:

https://youtu.be/GPhgxxwprA4

Hope it helps,

Thanks

you can use list to add item dynamically in fields.Selection 
cnt=0
list1=[]
for i in range(1900,2017):
         list1.append((str(cnt),str(i)))
         cnt=cnt+1

class Employee(models.Model):
      _name = 'employee.details'
      year=fields.Selection(list1, string='Years', required=True, copy=True)

     #append item

     list1.append(('118','2018'))

    #update item

     list1[0]=('0,'1899')

     #item updated automatically in field.Selection