How to Merge a Disk Partition
Methods
Partition-management programs such as Paragon Partition Manager, Easeus Partition Manager and Acronis Disk Director will merge disk partitions. These programs let you merge two or more partitions without reformatting the hard drive. Partitioning programs use nondestructive methods for merging partitions so that you will not lose the data contained in each partition.
Benefits
You can merge partitions to increase available system space when one partition is full. For example, if you store your operating system on one partition and your programs and files on a second, and the first partition is full, you can merge the two partitions to increase the disk space available to the operating system.
Considerations
Although partition-management programs preserve the data stored on each partition, you should still back up the data on each before merging the partitions in case an error occurs. For example, a power outage during the merger process could result in data loss on both partitions. Partition-management software also cannot merge partitions containing different operating system installations.
Source...