Easy to do and it can solve alot of problems.
Making garage door opening taller.
If you are lucky it s in good shape and either made from 2x12 s or even better a glulam beam.
Usually 4 or 8 feet.
Because garage doors are usually sized to snugly fit the dimensions of the garage itself making the door larger usually means making the garage larger.
I removed some siding and and re did the trim on the top of the door and then recovered every thing with aluminum and installed new rubber garage door sill around the opening.
The height of the rough opening must be 1 5 inches taller than the garage door you intend to buy.
That is the side where your truck is to go you can build out on the back side.
This means building a wall that spans the entire distance of the opening and is strong enough not to move until you are done.
That made my door height two inches taller.
Before removing the header you will have to support the roof above it.