Let's say I have:
key value
salt pepper
fish chips
vodka orange
rum cola
and I want the second column in uppercase.<F3> to start recording a macro. Alt →, → to position the cursor at "v" (or just →→→→→→ if this is a fixed width column), then Alt U to uppercase the next word. → to move the cursor one forward, to the start of the next line. <F4> to finish recording the macro.
Then press <F4> five times to run the macro five times.
(Explanation intended for users who've never used Emacs before. Of course, there are optimizations.)