It depends on 2 things.
1. The bedding you are using.
2. The size of your cage.
1.
Out of all of the beddings I would recommend Aspen or fleece. Aspen has no aromatic-oils, soaks up the urine and is perfectly safe for your guinea pigs. I usually put newspaper underneath the aspen as this way when it comes to cleaning all I have to do is wrap the whole thing up. I usually clean the cage out every 5 days, with spot cleans daily. The whole cleaning process involves me wrapping the aspen up in the newspaper, chucking it in the bin, sweeping out any stray pieces of aspen and using a 50% vinegar and 50% water to wip3 out the cage. After leaving the mixture to dry I then return, add a fresh layer of newspaper and aspen (a couple on inches thick), chuck out any left over pellets and fill that up, I finish by giving them fresh water. Aspen is quite expensive compared to other beddings but is well worth it. Fleece is a totally different bedding, what fleece does is wicks the urine through to the bottom of the cage. This is why you need to have some sort of absorbent underlay, good choices include towels, matress pads and puppy pads. I usually clean out the cage once a week (7 days) but I vacuum the cage every day to get rid of poops. Cleaning the cage when using fleece involves, taking the fleece and towels out and washing them in the washing machine with a cup of vinegar, I then put the fleece and towels in the dryer to get them dry quicker. After all of this is done I put everything back in the cage, change the pellets and give them fresh water. Fleece is quite expensive to buy but because you just re-use it, in the long run it is cheaper.
2.
Like Memphisgal said, the bigger the cage the less often you will have to clean it as they have more space to go so it isn't as concentrated in one spot. Alternatively you can try litter box training, this is quite hard to do especially with guinea pigs but none the less, it can be done. Litter boxes can be found at most pet stores (the ones that do not sell animals), fill the litter box with bedding (or litter but make sure that it is safe, I would stick to either fleece or aspen) and add some already soiled bedding to enforce the use of the box. If you do catch them using it reward with a treat.