Having problems installing update and changing text in signups

I have tried twice to update my membership plugin to 3.4.6.1 but it keeps saying failed.

The reason I am needing an upgrade is because I am getting several glitches with the signup process including: the page does not redirect to my welcome page after users have signed in; the text in the signup is not what I want it to say and I cannot find how to change it; when I enable invite codes, the field to enter the code does not show up in the signup form.