The MacBook Air I have only had a 121G SSD. I use it for music creation which uses a lot of memory. I needed a larger SSD.
Pretty nervous not going to lie. But not cause it was difficult just because it was the first time I had attempted anything like that before. Repair took 15mins and the time machine restore took about 1hr.
Once you open up your mac, Take a photo to see how everything is connected. This will help as a reference for when you put things back together.