Bitmaps are raster image files that use a grid made up of pixels. Each pixel has its own color information, and when the pixels are combined, they create an image. When a bitmap is enlarged, the pixels become larger and more visible, giving the image a grainy texture. Vector images are defined by paths, not pixels, so resizing one has no effect on the image quality. Converting bitmap to vector in Photoshop is not easy, but it can be done if you also have Photoshop's companion program Adobe Illustrator.
Open the bitmap file and use the Magic Wand or Magnetic Lasso tool to select the object that you would like to convert. In some instances, clicking on the object with the Magic Wand automatically draws a path around it for you. Other times, the Magic Wand has a difficult time determining the object's edges. If it doesn't work, trace the object with the Magnetic Lasso tool until it is entirely enclosed in a path.
Click on the Paths panel and choose "Make work path from selection" to make a copy of the path around your image. The button is at the bottom of the panel and looks like a circle with lines coming out from it.
Go to the File menu and select "Export." Select the "Paths to Illustrator" option to save the path and bring up the "Export Paths" window.
Name the file if you want it to have a different name than the original graphic. The default will be the original file name. The "Save as type" defaults to Adobe Illustrator (.ai). This is correct. Click "Save."
Open the file in Illustrator and clean up the path by adjusting anchor points or using the Smooth tool. Especially if you relied on the Magic Wand tool for your object selection, your image will have some rough edges.
This process works best on bitmap shapes with clearly defined edges.
Saving the path doesn't save the color information with the original bitmap. You'll have to restore any fills or outlines in Illustrator.