To delete a Classic Load Balancer, you can use Remove-ELBLoadBalancer; and to delete an Application Load Balancer, you can use Remove-ELB2LoadBalance. These cmdlets delete the specified load balancer from your account. The CNAME associated with the load balancer will no longer be available, and the traffic will not be sent to the target EC2 instances.
In the case of Application Load Balancer, it also deletes the attached listeners to ALB. You won't be able to delete ALB if deletion protection is enabled on the ALB. Both cmdlets will prompt for confirmation before the operation proceeds, unless you specify force switch. You also have to use load balancer ARN to delete Application Load Balancer. For Classic, you would be using the name of the load balancer:
PS C:\> Remove-ELBLoadBalancer -LoadBalancerName myfirstclassiclb
PS C:\> Remove-ELB2LoadBalancer...