It is better, to renew it now, and not to wait on the last minute. You have to make a new ios-distribution certificate in the apple developer console as explained in Erel's tutorial.
After that, you have to make a new provsioning-profile for all your distributed apps. It is not need to change the identifiers. Revoke the old distribution-cert could break exisiting apps, which are already puplished. You can also easily remove it after it has expired.
Before the old certificates expired, you have to comile your project with the new distribution and provisioning-file.