If you've overwintered in a greenhouse, repot your Fuschia with new soil in the same pot. This will give them fresh nutrients and remove salt buildup around the plant's roots. They like to be a bit rootbound, so wait and go bigger every 2-3 years or when your plant is wilting often.
When repotting in the spring, use a 2" bigger pot to keep the roots drier. (Too big of a pot could cause the soil to dry slower, which is not helpful.) Use a well-draining indoor potting mix with perlite to help with drainage.
Water your plant in the old pot before transferring over and let it sit for an hour. Place a piece of screening at the bottom of the container over the drainage hole to secure the soil and allow it to drain. Add soil to the bottom to elevate the root ball. Lift the plant and release the roots against the existing planter. Use a clean knife or garden trowel to wedge between the pot and the soil to loosen.
Inspect the root ball. Notice if there are any dead or rotting roots and trim them off with sterile pruners. If the plant is rootbound, cut through the roots to alleviate continued encircling.
Ensure the plant is sitting about 1" below the edge of the pot to avoid water spillage. Add more soil and backfill around the sides by tamping down. Fill up to the soil line but not over.
Water thoroughly, leaving the soil damp but not soggy. If settling occurs, add more soil.