What are the steps one should take to accept Mohammed as his prophet and spiritual leader?. What are the risks?

Let me start by saying that Muslims prefer to use 'believe' rather than 'accept'. Compare 'Accept Jesus' as Christians say. We prefer to use 'accept Islam'.

That noted, by accepting Muhammad(PBUH), I want to believe you mean, becoming a Muslim. You don't accept Mohamamed in isolation, you believe in Islam altogether.
This means you have to believe in Allah as your creator, believe in the messengership and prophetship of Prophet Mohammed and other prophets. You take guidance from the Qur'an.

Practically, after the mind work(belief), then you need to utter, with conviction the Kalimah i.e that there is no deity worthy of worship except Allah and Prophet Mohammed is His messenger.

With these you are alreday a Muslim and have 'accepted Mohammed', to use your word. Then follows practical aspects, praying, keeping to Allah's Dos and refraining from His Don'ts.

And at all no risk in believing in Him but benefit.

Benefit what?