How can I renumber the ordered list without changing each item?

[Юлия Басова]

For example, I have the ordered list:

1.1 A

1.2 B

1.3 C

Now I need to change the first number in my numeration to:

2.1 A

2.2 B

2.3 C

How can I do it automatically by specifying only the first number?