1. In the SPSS, choose [Analyze
->[Compare Means ] ->[Paired-Samples T Test] ]
If you wanted the one-tailed significance value, just divide the two-tailed value in half.
Robust t-test in R
The Wilcoxon Signed-Rank (nonparametric) test
Parametric tests such as t-test are based on assumptions about the distribution of the underlying population from which the sample was taken. The most common parametric assumption is that data are approximately normally distributed.
The Wilcoxon Signed-Rank (nonparametric) test is a non-parametric counterpart to the paired-samples t-test, which can be used in the case of the data is not normally distributed. The pros and cons can be found at https://www.mayo.edu/mayo-edu-docs/center-for-translational-science-activities-documents/berd-5-6.pdf