help with rmr 125 need asap as off work for next two days

hi there i have never worked on bikes but cars yes lol i need help as my rear wheel is shacking has a lil bit of play in it what do i need to do to fix this as it dont feel right when riding also i noticed the chain looks very slack could this couse the problem is it as simple as just turning the nuts on both sides to make it tighter will i need to change the bearings and one last thing the baffels in the exhaust how do i get them out as i want it to sound a bit meaner lol
thanks stefan
2008 superbyke rmr 125 :riding: