Use the following function:
DATEADD(type, value, date)
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date is the date you want to manipulate
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value is the integere value you want to add (or subtract if you provide a negative number)
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type is one of:
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yy, yyyy: year
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qq, q: quarter
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mm, m: month
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dy, y: day of year
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dd, d: day
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wk, ww: week
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dw, w: weekday
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hh: hour
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mi, n: minute
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ss or s: second
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ms: millisecond
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mcs: microsecond
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ns: nanosecond
SELECT DATEADD(dd, 1, GETDATE()) -- will return a current date + 1 day
http://msdn.microsoft.com/en-us/library/ms186819.aspx