Welcome the Technical Support section. Help us in assisting you by providing us with a concise and descriptive elaboration of your issues. Be specific and if possible, provide us with a step-by-step instruction in replicating your problem.
please goto joomla backend > extensions > languages > overrides, click New
and create new language string for:
MOD_COMMUNITY_LOGIN
MOD_COMMUNITY_SIGN_UP
for text changes no need to located the files. you can do it from joomla language overrides (steps in my prev post).
please elaborate more if I missing something.