The city is planning a City Hall Plaza makeover and has received a $155,000 state grant to design it. The new plaza will be focused on public gatherings, said Marc Resnick, director of Brockton’s Redevelopment Authority. He said there will be new brick paving, lighting, and landscaping. Money for construction will be sought from the state later. Brown, Richardson & Rowe of Boston will do the design work. The work will not affect the firefighters memorial.