Less than a year after the uprising started, Assad proposed a constitutional update that would have made the nation more democratic. The proposal went to a popular vote, where it passed handily. That vote and update was REJECTED by the rebels and west, who wanted an interim military government to take over the nation.
Contrary to popular belief, Assad technically doesn't meet the definition of "dictator". He's the elected president of a nation that conveniently only allows one party to hold power, and that has no term limits. Because he's the head of his party, it means that he gets re-elected forever.
The constitutional update made two important changes. First, it would have allowed true multi-party elections. Any party representing any political position could have run for votes. Second, it limited the presidency to two terms.
Why was it rejected by the west? Because it allowed Assad to finish his then-current term, which would have ended in 2014, and because it didn't prohibit him from running and trying to win the Presidency in an open election (and Assad has a LOT of supporters in Syria). As Obama said, the west saw it as Assad's "time to go" and wanted him gone RIGHT THEN, and wasn't willing to even discuss idiotic concepts like "a peaceful and democratic transition of power." War is much more profitable and politically useful.
Assad has stated that he's still committed to implementing the democratic changes that were made to the Syrian constitution, but that they can't happen while the nation is still in open conflict and while ISIS controls half the country.