How to delet un allocated drive from my HDD !

Hello,

I have recently purchased a 500GB Western Digital (WD) external hard drive. I creat almost 4 other drives out of it for the better management of my files. I did this partation by clicking the shrink commend.

I have two questions:
1. I delet one of the created partation and it shows as unallocated drive. How can i merge this partation with other partation ?

2. I have created other partation out of the 4th partation then again had to delet it. After i delet it shows free space and the partation box of the mentioned partation got green.

Looking foward your response at earlist.

Jseddiqi