Help for mediation

Hi, my research question is:
"Can we say that the number of hours of Internet use increases with Internet purchase? This influence of Internet purchase on the number of use can it be explained by an attitude becoming more favorable to as we know Internet? "
my variables are:
- Use of Internet per week (Use in hours)
- Internet attitude (Attitude_Internet 1 = very unfavorable, 7 = very favorable)
- If respondent has already made a purchase on the Internet (1 = yes, 2 = no)

I have to do a mediation in SPSS in 4 steps
(Variable z = mediator = Attitude_Internet
Variable x = independent variable = Purchase_Internet
Variable y = dependent variable = Use_Internet)

Step 1: The IV should predict the DV
Step 2: IV should predict the mediator
Step 3: the Mediator should predict the DV
Step 4: The effect of the purchase on the Internet on the number of hours of use will be increased when taking into account Internet attitude

But how can I do the 4 steps ? Should I use regression or anova ?
Thank you