First you have to edit your existing Ad by clicking on "Edit Ad" at the three dots at the top right of the Ad.
There is an option "Prolong/republish this Ad" with YES/NO switch. Click on "YES" option and then choose an advertising plan (duration) to prolong or republish your Ad.
There are three advertising plans: 7 days, 15 days and 30 days.
Each advertising plan costs certain amount of Partycoins depending on advertising plan you choose. See the price list for more information.
Keep in mind that no matter what advertising plan you choose the end time shall be calculated from current date and time +7/15/30 days.
E.g. if your Ad ends in 3 days and you prolong your advertising plan for 7 days, it means that your Ad shall be active for +7 days, not 3+7 days.
Every time you prolong/republish your Ad it shall go on top on Newsfeed.
You can decide to:
Read How to edit my existing Ad for more information.