You do this by assigning a character style to the glyph as part of your paragraph style(s) (if you REALLY mean "throughout") if you want it to ahppen automatically, or by using Find/Change to do them all, or a selection, manually.
How to add the character style to a paragraph style is a bit more complex and will depend on what else is in the paragraph that may need special handling as well as how many times the glyph will appear in any paragagraph. You can use either a "nested style" which can be used to do something like apply [None] up to 1<your Glyph>, then your new characer style through 1 character, or you can use a GREP style to find that glyph wherever it appears, or only when preceeded or followed by some other specific text and apply your character style.
Although they are a bit more intimidating if you think you can't write code (you don't really need to be a coder to use GREP), and they can slow down editing if you use a lot of them, GREP styles have the advantage that they can be applied on top of other nested styles which makes them a bit more flexible.
(In addition to Peter's)
There are two ways of changing 'the' size of any characters. First off, you can set the new size in points in the Basic Formats section of the Character style definition. But if you set it to '12pt' and this glyph appears in a 16 pt header, that will also be affected -- changed to 12 pt, that is.
A better way is to proportionally scale it, in the Advanced section. Set both Horizontal and Vertical scale in percents to the desired magnification factor (e.g., "125" to scale it up by ¼).