How do I change a file from GIF to SVG?

That's pretty hard, considering JPEG images are pixel-by-pixel and SVG images are shape-by-shape. There are two ways, though.

One, and the simplest, you can include the bitmap (JPEG) into the SVG file. Open Inkscape, and go to File > Import.... Select your image and it should appear in the page. Then open the Document Properties dialog in the File menu, and click on Fit page to selection. The last step is to apply the embed the image in the file: go to Effects > Images > Embed All Images..., leave both check boxes unselected and click on Apply. Then you can close it and save the SVG file.

The other way, you can try to figure out shapes from the JPEG. This is more of an art than a science, but a good starting point is an automatic rasterizer included in Inkscape, but which I can't remember the exact place of.

In any event, good luck. :)

@Andres, it's called Trace Bitmap and is in the Path menu. You need to File > Import your JPEG image first, then with the image selected use Path > Trace Bitmap. I almost always use the Multiple Scans : Colours with "Smooth" and "Stack" turned on. You may find it works better if you use a raster editor (like The Gimp, Krita) to "posterise" your image first.

HTH,

pbhj

Thanks Andres J. Riofrio, that solved my question.

Do I change a gif just like the JPEG file to a SVG??

Yes, Trace Bitmap can vectorize a gif image, just like jpg.