how can I go from Hong Kong Convention and exhibition centre to Regal Riverside Hotel?

You can take a taxi to reach Sha Tin and then take the East Rail Line to reach Hung Hom and change to West Railway Line to reach Tsim Sha Tsui. Then take Tsuen Wan Line to reach Admiralty and transfer to Island Line to reach Wan Cha. After you get out of the station, you can see the center.