When Reticle has a new version, the garage panel says so and its Download button opens this page. Close the game, get Reticle again from its page on the Mod Hub and extract it over the old files. A mod's file is named after its version: if it is left with two files, delete the older one. Only that mod changes; your settings stay in mods\configs\app.gunmarks.
Reticle needs no Gunmarks Core. app.gunmarks.core_*.wotmod is for the mods of 0.1.1 and earlier, which do: once every mod of yours is newer than that, delete it. The settings page says when.
From Gunmarks in one file: delete app.gunmarks_0.1.0.wotmod from mods\2.4.0.2. Each mod takes over your settings, the panels' places and your recorded battles on its first start.
After a World of Tanks update the game uses a new mods folder, named after its version: wait for the mod’s release for it.