To determine if you have a clog, first remove the attachment hose like you were going to put an attachment on. With the vacuum in the upright position, turn the vacuum on and place your hand over the hose. Do you feel a strong suction? If not remove the hose attachment by turning the locking ring at the end of the hose on the back of the vacuum counterclockwise, then remove the hose. Stretch the hose to it's fullest length several times. I would do this over some plastic or outside to keep the dust down.
Once you have done this replace the hose turning the locking ring clockwise to lock it in place, give the hose a little tug to make sure it's attached and locked.
Again, with the hose free from the agitator turn the vacuum on and fee for a good suction.
If you still don't have one then you likely have a plugged filter.
You will need to remove the dust bin.
Once the dust bin is removed, over you trash can empty it by pressing the dustbin door release downwards. Now rotate the dustbin lid counterclockwise to remove the primary filter. With the lid removed grasp the filter and turn counterclockwise to remove the filter.
Pull the filter out over a trash can. Once out inspect it, if it's dirty you should wash the filter in warm water until the water is clear. When finish let the filter air dry for 24 hours before reinserting it.
Upon reinserting the filter, turn it clockwise to lock it in place, install the filter cover with a clockwise rotation to lock it in place and reinstall the dust bin.
Now plug the vacuum back in and again with the hose removed from the agitator or brush and ready to install an attachment then the vacuum on and you should have a solid suction.
These vacuums are really prone to poor suction if the filter get dirty. Because they have washable filters, you should take time about one a month to clean the filters.