Under normal circumstances, you can replace or add new windows in the original walls of your house without needing planning approval. However, you may need planning permission if conditions were attached to the original permission. As long as your building isn’t listed, you should be able to install double glazing under Permitted Development rights, but do remember that for new or bigger windows or doors, you will need to follow Building Regulations guidance. Check with your local authority if you are unsure if there are any conditions attached or what they are, and remember that bay windows are classed as extensions.
Planning permission to insert a new window or door opening is not required as long as any upper floor windows on the side elevation are glazed with obscured glass (level 4 or 5 obscurity). They must also be fixed into a non-opening frame (unless the opener is more than 1.7m above the floor of the room in which the window is installed).