Best way to get felt off my flat roof to repair decking

[fleeced]

I have a couple sunken areas on my flat garage roof and it appears the straw like decking has split underneath.

I plan to replace these with some OSB3 panels and then put felt underlay and overlay on top.

What is the best way to remove the existing felt and damaged decking?

Do I work on the split decking from below and try and make a hole through the felt? Don't want to damage the beams it is attached to, I assume by nails.

Any help, advice welcome. As I am a DIY novice and a bit nervous about getting on the roof and doing this

 

[Mw Roofline]

Get it off with a spade/shovel then once you have got a section off you can use crowbars etc...