You can indeed convert a jpeg to a vector file in Inkscape, and I often do when I want to make modifications. For example, if I want to remove some strokes from an abstract design, or add cutlines around a design (for an ornament, ETC).
To do this, drag your .jpg or .png into a blank Inkscape document, and import using the default settings (at least I’ve never found a need to change them.) Then with the jpeg selected, go to Path->Trace Bitmap (or shift+alt+B). Check the box for ‘Live Preview’ (near the bottom, to the right of the controls box). There are a couple different ways to execute the conversion and you should play with them to see which gets you the results you’re after.
The end result is that everything you’ve converted will be nodes and handles, and you can remove any bits you don’t like, or add/adjust other elements.
Cheers, and good luck!
Edit: I should add that once the conversion is done, you will be left with both the original jpeg and the nodes from the conversion, so don’t forget to delete the original jpeg object.