I changed my admin account to no password help?

Just started using Ubuntu today, completely deleted windows 7. It works way better, heres the issue: I changed my admin password to no password because i got tired of entering it for everything everytime my computer went to sleep mode, now i can't download anything from the software center because it keeps asking for authorization, and a password, which i do not have now. I put in the old password, that didn't work, i tried to get into grub or recovery mode, and when i hold down or push shift, the computer just starts normally, nothing happens, UBuntu is the only operating system on my computer now, so i don't know why shift won't work. I can't change it with terminal either, I tried, maybe I am just stupid, but nothing I have read on the internet works for me. I Just want to download stuff from the software center, and I don't have a password even though it keeps asking me for one, what can I do? do I need to reinstall Ubuntu? don't want to but I will if I have to, someone help me if you can please, its driving me nuts already devoted a few hours to trying to fix it.
Thanks in advance.