Sound in the Lacetti or radio and loudspeaker

Hello guys! can someone get me better speakers for ‘n Lacetti BJ 2005?I got an AEG Radio 400 W, BT, SD slot, USB, uwm.The sound is not so bad at all but would like to steal the best from it. so I imagine: Keep the series LS in the front and replace the rear with 150W or 160W. or the 4 with 100W each. what do you think? Could it work or am I wrong? At an understander & what of course I thought but rather stay with the 1st choice there I save myself the stress and the costs for a hi-fi business. Otherwise I will leave it that way against my will. Thank you very much in advance The best