Paint and Notepad are the two small and lightweight tools Microsoft Windows offers to edit simple images and texts. The former allows the manipulation of plain pixels, the latter the manipulation of basic ASCII texts. In Linux you will probably use GIMP and GEdit instead (at least if you are using Gnome or Ubuntu). GEdit is a very simple text editor, just like Notepad, and a bit more comfortable than VI or VIM. GIMP is the Linux equivalent of Microsoft Paint, a simple GUI application to do basic image manipulation. Sometimes you don’t want heavy applications to create WYSIWYG texts or sophisticated images. You just want to add or remove some characters or pixels. Enlarging or shrinking an image in GIMP seems to be complicated at first sight. Yet it is as simple as doing this in Microsoft Paint.
Load the image you want to enlarge with GIMP. Choose the menu item ‘Image > Canvas Size’. In the opened Resize Dialog, select a new Width or height (if you click on the chain symbol and break the chain, you can set Width and Height separately). Then click ‘Resize’ to close the dialog. Now choose the menu item ‘Image > Flatten Image’ and you are done: you have got your old image embedded in a larger picture. The same method can be used to crop or shrink an image.
That doesn’t make the picture larger, just the canvas.
Your title is very misleading. “Enlarge an image in GIMP”