To change the hose on a Shark canister vacuum cleaner, press the two tabs at the bottom of the nozzle on the back and pull the hose off. Then, insert a new hose into the nozzle while squeezing the tabs, and release them when done.
Next, disconnect the hose from the canister by pressing the tabs together and pulling up. Also, detach the hose on the motorized floor brush at the top by pressing the tabs together and pulling out. Pull out the connector at the bottom, and Insert the wide end of the hose into the connector to reattach the hose.
If the vacuum cleaner is losing suction or not picking up dirt, check the hose for blockages. Detach as above and clear any debris from the hose, and reconnect it. If the vacuum still isn't working properly, the hose is probably damaged and needs to be replaced.
Replacement hoses for Shark vacuum cleaners are available on Amazon and other online retailers for about $40 to $45 as of June 2015. If the hose is damaged due to normal wear and tear and the vacuum is under warranty, the manufacturer typically replaces the hose at no cost to you.