Bungalow repair

I'm in the midst of renovating a 40 year old bungalow. It hasn't been looked after for quite a while. I removed some rotten weather boards from the lower third of the exterior walls and have found that underneath the bearers are fine but the two problems are 1. dry rot has attack one floor joist and
2. the floorboards around the entire perimeter are rotten. ie between the ends of the floor joists and base of the walls. This was confirmed by removing the old lino on the floor of the bungalow which showed the perimeter is rotten.

My question is, how would I go about safely removing and replacing the boards underneath the walls??.

Any advice would be greatly appreciated. Thanks:U

Posting some pics would give a better idea of it.