upper left, upper right

Hyphenate as adjectives. Use instead of top left and top right.

Example
The upper-right corner

Accessibility note Don't use directional terms (left, right, up, down) as the only clue to location. Individuals with cognitive impairments might have difficulty interpreting them, as might people who are blind and use screen-reading software. It's OK to use a directional term if another indication of location, such as in the Save As dialog box, on the Standard toolbar, or in the title bar, is also included. Directional terms are also OK to use when a sighted user with dyslexia can clearly see a change in the interface as the result of an action, such as a change in the right pane when an option in the left pane is selected.