With MIS Synchronisation, ideally, lesson changes should be actioned in SIMS, however, there is a potential way around this...

If you want to remove all lessons for a particular date, this can be quickly achieved by going to Administration->Academic Settings->Holidays & Closures. Here you can set a date to a non-lesson day, but still allow bookings.

If you only want to remove some lessons though, things get a bit more complicated...

1. Go to Administration->Academic Settings->Academic Manager and select the Lesson Timetable option.
2. Find the first applicable lesson and click on it.
3. You'll now see a page listing all individual dates that the lesson applies.
4. On the row covering the date that that you want to remove, switch it over to No Lesson.
5. Over to the left is a 'Slot Protected' option. Setting this to Yes means that the next sync won't undo the changes just made.
6. Click Save and repeat parts 2-5 for each other lesson that needs to go.
   

We wouldn't recommend this second method if there's a huge amount of lessons involved though. It's going to be a lot quicker/simpler if those changes could be logged in SIMS.