When you develop a custom SharePoint Timer Jobs sometimes you may need to delete junk jobs created by deployment times. This article will explain you how to remove custom timer job.
About Timer Job:
A timer job runs in a specific Windows service for SharePoint 2013.
Timer jobs perform infrastructure tasks for the Timer service, such as
clearing the timer job history and recycling the Timer service. Timer
jobs also perform tasks for web applications, such as sending email
alerts.
How to remove by C# Code: You must use a Visual studio project to create timer job where you will uncomment the following code from TimerJobFeature1.EventReceiver.cs
// Uncomment the method below to handle the event raised before a feature is deactivated.
public override void FeatureDeactivating(SPFeatureReceiverProperties properties)
{
SPSite site = properties.Feature.Parent as SPSite;
// delete the job
foreach (SPJobDefinition job in site.WebApplication.JobDefinitions)
{
if (job.Name == List_JOB_NAME)
job.Delete();
}
}
Then You will Retract the solution. Timer job will be removed from the Timer Job List.

DONE!
How to remove by PowerShell Command:Find timer job ID by List_JOB_NAME using command.
Get-SPTimerJob | where { $_.name -like "*<List_JOB_NAME>*" } |ft id,name
Set job to a variable
$job = Get-SPTimerJob -id <GUID>
And delete it.
$job.Delete()

Hope This will help you.
Cheers!!
Find more reference:
http://technet.microsoft.com/en-us/library/cc678870.aspx
http://msdn.microsoft.com/en-us/library/hh528519%28v=office.14%29.aspx