Agree with Colin and Ioneabee ... looks like the wall is an external wall at 1st floor level (easy to check) ... rule of thumb is leave minimum 600 mm of wall at each end of new opening ... I would want to visit site before designing the relevant support for the loading that will be applied ... it depends on so much more than span of lintel such as 1st floor joists span and direction, roof loading including snow load from garage roof, any openings above the opening you are proposing, ground conditions and existing foundations etc.
You will need Building Control approval and they will need calcs from a qualified person ...