Hi Salman,
there are several Things you can do:
1) wait for 10 days of inactivity of your instance then it will be claimed back to the pool and you can request a new one
2) take a look at the "Instance Help Forum" at https://community.servicenow.com/community?id=community_forum
3) See PDI Guide "Getting Instance Assistance" at https://developer.servicenow.com/dev.do#!/guides/sandiego/developer-program/pdi-guide/getting-instance-assistance and what things you can check on your side
Hope this helps....
