If you do go with water cooling you will need a case that has rubber grommets, and you will be installing outside as well as inside the case, I really can't recommend this for anyone but enthusiasts, or as a way to solve a serious heating problem, but have we even identified that it is that serious yet.
For case fans, depending on the case you have there is usually the option to install more, this is a more straightforward solution, the bigger fan the better as a big fan rotates slower and makes less noise. a new CPU cooler may be necessary as well, can't say until we know how hot is 'hot'
And yes, house cleaning inside the computer, necessary once in a while, small fans and heatsinks get clogged with dust reducing their efficiency. I just use a fine haired brush, never did find anywhere here that sold those compressed air thingies.