Hello there Tiula, and welcome to Anim8or Forums,
,
If you want to delete a frame in sequence mode, select the frame and go 'Edit -> Frames -> Delete selected. Theres other options for frames there as well.
But you might not want/need to actually delete a frame. You can delete, copy or paste the key(s) from 1 frame to another. Just open the timetrack to find and select the key(s), then copy/cut/paste or delete as per normal.
(select a key by going to frame, then select the actual key in the left of the timetrack, by clicking the name of the bone that contains the key)
If you ever need to select multiple frames, (perhaps containing multiple keys), select 1st frame or key that you want to edit, hold down 'shift' and click last frame of selection.
This all applies to Scene mode as well as sequence mode.
