It’s a big question and takes time to answer. Some things to consider in trying to figure this one out:
What is the right amount of space?
Is there enough space for now? Is there enough space for five or ten years from now? Will you be able to grow into the house? Does it offer flexibility? Would you like space for a home office?
Is the style of the house important to you?
Do you have a dream of living in a Victorian or Brownstone? Or are you mostly looking for space and the style of the home is less important?
Does the current layout work?
If not, what kind of a renovation would you consider – just touching up the finishes; fixing up the kitchen and baths but keeping room arrangements and layouts as-is; a complete gut renovation where you start fresh with almost everything?
How old is the house?
If the house is over a certain age and has never been renovated, it is probably a good idea to at least update all the plumbing and electrical. That will likely require a more significant renovation because replacing plumbing and electrical requires opening up a lot of walls, and once that is done other issues could become apparent, such as structural or water damage. So, for an old, unrenovated home you should be ready for significant work.
Will you be able to make the modifications to the space that you are hoping for?
You may want to open up a space, make some windows larger, or relocate a bathroom. These kinds of changes require removing portions of loadbearing walls or relocating plumbing lines. Is this possible? How much might it cost? Will you need permits for this? An early consultation with an architect can help you understand what is possible and what would be involved.