If you're looking at this guide, you've probably encountered this issue:
you're trying to adjust the windowed resolution, only for all your methods to be met with it changing back to the original anyway every time it transitions to the menu or the game itself.

Unlike most other games you're probably familiar with, Tomb Raider 1 not only has no in game resolution setting, but it also relies on 2 separate settings for its resolution.

The first one you've probably already found on your own, and can be found in the file: "dosboxTRWindowed.conf" (which is located in your game folder) look for the setting: "windowresolution" it's likely set to "original" which as far as i know is a whopping "320x240" set this to whatever you like. This setting is used for cut scenes

Now here's the bit that people tend to stumble over. In the same folder as the previous file locate "glide.ini" and change the resolution option to just the width. the height gets calculated automatically using the aspect ratio. this setting is used for all interactable parts of the game.

Et voila the game now no longer becomes smoll and stays at the desired resolution.