[SalesForce] How to get the end date of a scheduled job which was scheduled via System.Schedule

You can do either option (both are viable).

To specify a run-once schedule, specify a fully qualified date and time, such as:

0 0 0 4 JUL ? 2014
| | | | |   | |
| | | | |   | \------- YEAR (2014)
| | | | |   \--------- DAY_OF_WEEK (NOT_SPECIFIED)
| | | | \------------- MONTH (JULY)
| | | \--------------- DAY_OF_MONTH (4th)
| | \----------------- HOUR (0- MIDNIGHT LOCAL TIME)
| \------------------- MINUTE (0)
\--------------------- SECOND (0)

This would run at midnight of the scheduling user on the Fourth of July this year, and never again.

If you want to kill other jobs, you simply query for scheduled jobs that are not already cancelled, and then call System.abortJob on those ID values. See CronTrigger for more information.

Finally, you can also abort the current job in the execute() method:

public void execute(SchedulableContext sc) {
    // Do stuff here
    System.abortJob(sc.getTriggerId());
}

You cannot update the scheduled jobs. You need to delete the existing job and then schedule it again.

To Delete existing job follow below step:

Setup -> Scheduled Job -> Job Name -> Delete

Now to schedule it again:

Setup -> Apex Classes -> Click on Schedule Job -> Select your class name and give other values