Generally if your bottom bracket is creaking or crunchy when cranking up a hill then it's time for a new bottom bracket. I learned everything I need to know about bottom brackets from Sheldon Brown and his website is here.
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Step 1: Right Tools for the Job
Look up what model bottom bracket you are going to need to install for your bike. Obtain a bottom bracket tool and bike grease. Once you have those, left up your sleeves and let's get started.
Step 2: Take Out Old Bottom Bracket
Take out old bottom bracket and clean out the old grease with WD-40 or brake cleaner. Be sure to wear a mask and protective eyewear.
Step 3: Install New Bottom Bracket
Place in new grease into the bottom bracket (Spread evenly) and install new bottom bracket.
Step 4: Reinstall Pedal Handle
Put back on pedal handle and now your bike is good as new.