That will depend on what the transmission is in. In most cases you have to drop the pan, but there are now some that have drain plugs. And the filter in a transmission is up inside of the transmission. No two are quite the same.
Get a service manual and read it. Like Kirk said it would help if we knew which transmission. Most will need the pan dropped to change the filter even if there is a drain plug. If you are not familiar with this best to have someone perform the job. If the filter is not installed properly it will ruin the trans. Some like the Allisons have external filters.