How to migrate column type from uuid to serial

[Hemil Ruparel]

I was integrating a payment gateway for my app when I noticed its maximum
length of customer id string is 32. SIze of UUID is 36 (32 characters and 4
dashes). So I want to change the type of customer id to serial. The problem
is by now, the column is being used at many places. How to migrate the
column to serial without dropping the data?