Even if the GUI tool runs perfectly to remove the Replication components, it will still leave elements behind.
The most common items that are left behind are:
1) database options
2) replication objects
3) sysobject settings
4) rowguid column
5) conflict tables
6) distribution database
To remove the database options, you simply execute sp_dboption for published, merge publish, or subscribed, and set it to false.
exec sp_dboption 'pubs','published', FALSE
Removing the sysobject settings is more involved in that you have to turn on allow updates, update the replinfo column and set it to 0 where it is 128, and then turn off allow updates. At this point, you should have a fully functional database that allows you to alter/drop objects and drop databases. You could stop here without having any side effects. But, we might as well take everything out. You get rid of the rowguid column, if it exists, by altering the table and dropping the column. Conflict tables are simply user tables and can be removed with a simple drop command. The same goes for any triggers, views, or procedures that replication created.