Increase length of Loft Hatch space for new door

[ric1981]

Hi,

I need to increase lengh of the existing hatch in order to fit a new new door. I am attaching graphic.

https://ibb.co/p0jjPyW

- The green in the middle is existing hatch space.
- Thick Black bars are Big Joists.
- A bit smaller gray bars are smaller joists.
- The red square is the one I need to cut in order to increase length of the green hatch space.

My question is what is the best way to put new joists in? I am newbe diyer so any tips are also welcome.

Thanks

 

[foxhole]

As plan, you need to extend the left side up to large timber and then you can remove small centre top timber .
Only one pic?