Cyclo Vac recommends you replace the vacuum's filter-bag once it's full. Depending on the use of the central vacuum, frequency will vary. The GX series models have an integrated monitor that will signal when comes time to replace the bag.
First, remove the vacuum cleaner dust canister.*
Withdraw, seal and throw away the old bag.
As you put the new bag in, make sure the bag's grooves are aligned with the indentation on the adaptor.
Insert the bag completely (until it reaches the retention ring). Then, to insure the filter-bag stays in place, rotate it 20º.
Put the vacuum cleaner dust canister back in place.
*To change the bag on the Axess and GS111 models, remove the power unit's top cover rather then removing the dust canister.
Also, be sure to change the disc-shaped filter (between motor and filter-bag) after three filter-bag changes.
Use exclusively Cyclo Vac filter-bags. Failure to do so could void the warranty on your central vacuum.