You have forgotten to post the used version of UltraEdit and the used GUI mode. So I assume currently latest version UltraEdit for Window v24.20.0.30 used in ribbon mode which is not my preferred GUI mode.
There is on ribbon tab
Edit in group
Select and delete an arrow below third item
Delete which opens on click a popup menu with menu item
Delete to start of line. This command has by default the hotkey assignment Ctrl+F11 as shown by the tooltip. The hotkey can be configured at
Advanced - Settings or Configuration - Key mapping. This command is for deleting in current line everything from current position of caret to start of the line.
In column mode after having created a no-width rectangular at a specific column, press Shift+HOME or twice Shift+HOME to select in column mode everything to column 1. Then press key DEL to delete the rectangular selection. The behavior of key HOME can be configured at
Advanced - Settings or Configuration - Editor - Miscellaneous with the setting
Home key always goes to column 1. Click on button
Help for a description of this setting after having opened the appropriate configuration dialog.
But there are much better methods to remove indent spaces than using column mode.
Programmers simply select in normal text editing mode one or more lines and press Shift+TAB to
decrease the indent by 1 and just TAB to
increase the indent by 1. The settings at
Advanced - Settings or Configuration - Editor - Word wrap / tab settings define based on file extension if the indent is done with tabs or with spaces and how many spaces represent a tab respectively an indent. See topic
File extension based word wrap, tab and indent settings for details about this configuration.
And there are on ribbon tab
Format in first group
Indent the two commands
Indent Selection and
Remove indents (two small symbols right of large
Reindent Selection item) to add/remove
X number of spaces from selected lines in normal text edit mode. I use never those two commands as TAB and Shift+TAB are faster to execute by key.