You'll need to replace your fittings and hoses with 1.5 in fittings. Here is what I'm using when I decide to change mine
You'll need three of these -- two inlets and one outlet
Amazon.com: Hayward SP1023 1-1/2-Inch FIP Inlet Return Fitting with Locknut and Gasket: Garden & Outdoor
www.amazon.com
One of these for your outlet, where the water comes back into the pool
Amazon.com: Hayward SP1419D White 3/4-Inch Opening Hydrostream Directional Flow Inlet Fitting with 1-1/2-Inch MIP Thread: Garden & Outdoor
www.amazon.com
Two of these for the inlets, where the water leaves the pool going to the filter
Amazon.com: Hayward SP1419E White 1-Inch Opening Hydrostream Directional Flow Inlet Fitting with 1-1/2-Inch MIP Thread: Garden & Outdoor
www.amazon.com
Three of these, to reduce the 1.5 fittings to 1.25 fittings
Amazon.com : Swimline Hose 1 1 Adapter, White : Intex Pool Drain Hose Connector : Sports & Outdoors
www.amazon.com
You only need these if you don't have 1.5 in hoses for the filter.
There are videos on YouTube that show how to put in the new fittings. Basically you use one of the new gaskets as a guide, mark around the hole in the middle of the gasket, cut the hole, then fasten on the first fitting. Everything else screws into the first fitting.
Take your time, measure three or four times before you cut, and be courageous.
Good luck to you
and me!