Lintel question for a bungalow window

[Swell1]

Hello, we plan to remove a small window and external door and make it in to one large window.
Re the lintel, do we require a structural engineer inorder to buy the correct lintel or can you work it out yourself? Any advise appreciated. Thanks

 

[^woody^]

If you use a suitable standard off-the-shelf lintel, fitted in accordance with the manufacturer's instructions, you don't need to provide calculations.