I have a door opening on a bearing wall about 36 inches, and I would like to make it about 6 feet wide. Can this be done and Any suggestions on wood size I should use?

The standard header size for a 6' door in so. cal. is a 4X8. The direction that your roof trusses run will make a difference if they run perpendicular to the wall. Once you open the existing wall... the path to framing the wider opening should become pretty clear.

Good Luck

oops... if the existing wall is framed with 2X6's... you'll probably have to use a 6X6 header instead of a 4X8.

the wall is framed with 2 X 4's and I checked the measurements the largest header I could use is a 4X6 with the door way height staying the same. Will the 4X6 be OK to use?

Yes... The standard rule for header sizes is... 4X4 for a 4' opening... 4X6 for a 6' opening... etc.

The reason I recommended a 4X8 is the "load bearing" part. I always tend to lean towards over-engineering just to be safe. A 4X6 should be fine but do use TWO 2X4 trimmers and maybe even a double king stud.

The Header Should Be Made Of (2) 2x10x6 Plus And Extra 2" For Your Rough Opening, The Extra 2" Is For Shimming When You Install A Door Or Window
So Total Length Will Be 74".
As For Constructing This Its 2 2x10x6 With Osb 1/2 Between Them, You'll Also Have A 2x4 On Top And Bottom Of The Header.

To Install It, You Need To Build A Temp Wall Under The Ceiling Joist To Support The Load While You Taking The Header Out And Putting It Back In,
Use A Towel Or Someing Soft On The Ceiling So You Don't Mare It Up When Your Building The Wall.

As For Tools, Skil Saw, Hammer, Nails , Pry Bar, And Most Importantly A Sawzaw, If You Don't Have The Last Tool Don't Even Try It, You'll Just Frustrate Yourself, It's a Remodelers Best Friend.

But That's It, Id Say Allow At Least A Half Day For This Unless Your Fairly Handy