If you can't get in via your lock code, you will need to wipe the device to get back in. Use iTunes and backup the iPad if you don't already have a backup. If you have an iCloud backup that will work as well. In iTunes restore the iPad and when it comes back up select restore from backup. Select the latest backup and during the setup process you will be asked for a new lock code.
If you have not backed up the iPad to iTunes before then you will not be able to back it up there because iTunes will tell you the iPad is locked with a passcode and needs to be unlocked first. If that is the case then just use your iCloud backup to restore the iPad.