There are so many software's available in the market to vectorise images. But you can do vectorisation in Photoshop itself. It's simple and takes only less than a minute. Here it is!

• Open the Image in Photoshop
• Go to Filter --> Artistic--> Cutout
• In the Cutout menu select Poster Edges and make sure that Edge thickness is 2 , Edge Intensity is 1 and Posterization is 2 . Click ok
• Goto Image --> Adjustments --> Brightness/Contrast
• Set Brightness to 10 and Contrast to 30
• Again Go to Filter -->Artistic-->Cutout
• In the Cutout menu select Cutout and make sure that the Number of Levels is 4 , Edge Simplicity is 4 and Edge Fidelity is 2 Click ok

Your vector image is ready :-)  Feel free to ask you doubts as comments below !