Tier 2 general extension

Hi guys, I'd like to know how to extend my tier 2 general visa. My current visa is going to expire at the end of August and I am living in the uk. According to the home office website, I can do it via the online form, priorty service or preimer service, if I am correct?
Also, I want to know more informtation about legal representative. Do I need one or what? As on the online form, it asked me if I have got one or not.

Thannks

1. Extend your visa
2. Guidance on application for UK visa as Tier 2 worker
3. If you think you are capable of ... understanding the requirements, gathering the documentary evidences, and making an application ... on your own, then you don't need a representative.