Change SQL Server Service Accounts

Hi,

We have taken hand over of a SQL Server 2014 instance recently. Some of the SQL Server Service is running under 'nidadmin' windows user. We want to disable 'nidadmin' windows user and want to change the account of the SQL server service to 'NT Service\....' 

1) How to change the service account (detail step please).

2) Is there any impact if I change the service account?

3) Do we need to restart the SQL Server Instance for this?

4) Do we need to change anything anywhere else?

Here in below picture green marks account need to be changed to  'NT Service\....'