Getting Rid of Unwanted Tenants

[Brian Washburn]

I am currently working on purchasing my first rental property and it has tenants living in it with a lease through the end of August. The tenants have said that they want to renew their lease for another year, but when we went to look at this property they left bongs, pipes and torches laying in plain view. One bedroom smelled like it had weed hidden all throughout it. They are very messy and have clutter laying all over the place. 

I like that the house has tenants for the first few months I own it so I don't have to worry about finding someone right away, but I do not want to renew these guys come August. I know I need to educate myself on Nebraska tenant laws, but my question for now is:

Do I have the right as the owner to just give them 60-day notice and tell them I am not interested in renewing their lease and they have to go in August? Are there any laws that would force me to let them stay? I also want to raise the rent by about $300/mo (it is currently way under market). Is there anything that would legally block me from doing that?

Finally, what is the best resource you have found for educating yourself on landlord/tenant laws?