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First, changing a bank statement in any way might be viewed as securities fraud or financial fraud, I have to warn you. A bad example of this is the complete crash and ruin of Peregrine Financial, whose head was the only person who read the actual paper bank account statements, and who changed entries to show money that wasn't in the accounts any more. He is now doing hard time for pretty much the rest of his life.
Second, if you insist for whatever reason on altering a bank statement in any way, even just cosmetic reasons, there are many graphics programs available that can alter or edit electronic copies of documents. Even just the basic Paint (or in Windows 8.1, 'Fresh Paint') program(s) provided with Windows can do something of the sort. For the advanced video editing functions, there are many programs from Adobe - esp. Photoshop, which has given us the term 'Photoshoppping' for any editing or retouching or insertion into a photo - that are thorough and professional, albeit much harder for a beginner to use.
Then, for the open-source software aficionado, the 'Gimp' program is pretty much the standard. Though again, it is somewhat hard to use for a beginner.