Google NPTC, Chainsaw related operations.......cs30 & cs 31. Chainsaw maintenance,cross cutting and felling small trees (up to 18" dia)
You will need to get these done before you can go any further, ie climbing, dismantling, large trees etc
Courses will be easy to find and run often.
However, it will set you back in excess of five hundred nicker, unless you can get funding/grant.