the SERV and ABS Light in my Renault Laguna Dynamic 2002 has come on?

I have recently had my spark plugs changed at a garage who advised that this was the cause of the car stuttering as soon as I changed gear. I also had my tyres replaced. One week on and my ABS and SERV light has come on. Can anyone tell me what they think is going on before I go back and shell out another load of money as I haven't got a clue about cars and am worried that I may be told any old story.