If the partition in question is directly after your primary partition, you can use the Disk Management tool to extend it.
Backup any data on the secondary partition
Start > RIGHT click Computer > Manage > Disk Management > Find your disk > Right click on the partition AFTER your boot partition (your C: drive) > Delete the volume entirely > Right click on your primary partition > You should now be able to extend your partition out to the old space.
If the partition is NOT directly after your primary partition, you will need to get a program called EaseUS Partition Master. It is a very useful tool in completely reorganizing your partitions the way you want.
A word of caution - because you are messing with partition tables and, depending the circumstances, moving data around, it is highly recommended that you back up all data first, as there is a rare chance that you could wipe all the data and/or break your hard drive's partition table using this tool if it is done incorrectly or the system shuts down while in process.