I'm a web professional, recently we wanted to make major changes into our web app and one of our colleagues used the word
house cleaning. What phrase do you use to say major changes need to be done. Can we use
house keeping? What is the difference between them?
The word housekeeping normally implies things that are done on a regular basis to keep things a house clean and organized -- or, in the case of a computer system or software, keep things running smoothly.
(House cleaning is something that a cleaning service does.)
It's not exactly the same, but the phrase "to clean house" has a slang meaning of a fairly indiscriminate removal of unwanted things. So it sort of applies, but I personally would use overhaul (completely re-do), redesign (major feature or look/feel changes), or refactor (optimize the underlying software without changing features) for what you're describing.