I have SharePoint 2013 post installed with a single account which runs all SharePoint services.
Now I want to apply the best practice SharePoint 2013: Service Accounts on the SharePoint server by using a different user for each service.
it is healthy practice to use separate accounts for services. As you mentioned you are running the farm with single account and we treat it as a Farm admin account which will run Central admin app pool, SharePoint timer service, Application discovery and load balancer service etc.
For changing the service accounts, I would follow these steps.
- create new service account in AD
- register those accounts inside the SharePoint as Managed Accounts.
- set the permission on the Config db as well as other related services or content databases.
- Now you can change the most of the services account i.e App pools, Service application etc from central admin. central admin > security > configure service accounts. select the service from 1st drop down then select the account from 2nd drop down. this is the guide
Also check this guide to change the service accounts: Service Accounts and Managed Service Accounts in SharePoint 2010