If you had to choose a program to use for changing case (UPPERCASE, lowercase, Sentence case, etc.) Microsoft Word works best in most cases. It has several options available, and the changes you make are retained if you copy and paste them.
But Excel can be useful at this task too, if you understand how it works. Not only will it save you time, it eliminates the chance that you'll introduce a mistake by retyping the text. This can be particularly helpful if you ever need to change the case of text in a language you don't know; all of the accents and other diacritical marks are retained.
If your text is in a cell, you can use simple formulas to convert it to ALL UPPERCASE, all lowercase, and Proper Case (All Words Start With A Capital).
Here's an example of these three functions in action:
The text returned by these formulas will be retained if you cut and paste the strings into another program, but you'll still have the text you started with in the original cell (A1 in the example above) if you need it.
If you're working in a text box in Excel, you can select the text you want to change, right click it, choose Font, and check All Caps:
Click OK and your text will be ALL CAPS. However, if you cut and paste the same text anywhere else, it will retain its original capitalization scheme. This could come in handy if you want to change the appearance of the text visually in an Excel text box but keep the original string intact for future use. If you ever want to make the change permanent (or choose a different capitalization scheme), it's easy to copy and paste the text into Word and adjust the capitalization there using the Change Case button on the Home tab:
Then simply paste it back into Excel or wherever you need it.