How to change the date of scheduled tasks?

Hi all,

In my piwik, the scheduled task of purges (…\CoreAdminHome\Tasks.purgeInvalidatedArchives, Tasks.purgeOutdatedArchives) are planned weekly , and next occurrence will be tomorrow in the morning. Tomorrow is also the first day of the month, where other specifics treatments are programmed.
Is there a simple way to move the date of this purge to next monday for example ?

Thanks for your help