How to you call the process when you COMPLETELY change everything in your house or flat?

Question

Answer

If you change all the THINGS in your apartment, but do not change the structure I would say you are REDECORATING.

If you do simple construction such as painting I would say RENOVATE.

If you build or remove walls then I would describe it as REMODEL.

Answer

It is usually called "redecoration" or "renovation".

Answer

Refurbishment/renovation and the result is - freshly refurbished.