I am not able to extend partition in windows server 2008. We have two different partitions which we want to join and make one partition. I came to know that basic disks have limitation of 2 TB each partition and we can create a maximum of 4 partition due to limitations.
Yes, your data will be fine, though you should always ensure your backups are maintained and up to date before doing such critical operations.
Here is a Technet article which will guide you through the process and some key considerations:
I think minitool Partition Wizard do this http://www.minitool.com/partition-manager/partition-wizard-home.html