Problem with the post date on wordpress.com, need help

I have a few blog sites running on wordpress.com using posts, the serps results show the outdated date, if i change the post date, will it affect the rankings?

Be careful if you have year/day/month in your url ( /2015/15/12/postname , /2015/postname, etc). If thats the case you'll have to 301 redirect the old url to the new one or else you'll most likely lose you rankings. It's easy to setup redirects on self hosted WP but I don't know about wordpress.com

Removing dates will have a positive impact over ranking.

i dont think removing date will be of any benefit at all in terms of ranking, i would say otherwise actually. it may impact user experience or direct traffic if url is easier to remember, but not a big deal. remember to check if old url redirect to the new one if you make any change to your wp permalinks.

also, updating posts with newer or fresh content, will help your rankings on serps